Considering it was the first day of class with new people, the student probably did both things.
And it is highly likely that his boasting attracted the other female student.
Subsequently, that female student approached him, certainly with an intention that was not pure. The reason Arthur determined that her intention was not purely to make friends was because of the surprisingly rapid increase in her intimate expressions.
He called this phenomenon the "Increase in Expression," a psychological indicator that reflects the level of closeness between two individuals, mirrored by the frequency and amplitude of their behaviors.
According to the Social Penetration Theory (Altman & Taylor), the development of social relationships typically occurs gradually, through a process of disclosure and feedback; that is, behavior increases with the accumulation of trust. A sudden disclosure, bypassing the natural pace, often hides an ulterior motive.
The Increase in Expression, for Arthur, is the metric for assessing the level of intimacy between people. The closer one is to someone, both physically and psychologically, the more "facets" of that person are expressed, which also means a greater volume of actions.
Here, a distinction must be made with extroverts to avoid unnecessary misunderstandings.
An extrovert exhibits many actions, but those actions are largely for themselves, not for others—for example, hand gestures while speaking. This is a performance by the subject, made consciously by the subject, and only the latter part is for interacting with others.
Extroverts tend to display a lot of behavior, but it is behavior that is primarily self-activating of emotion.
In contrast, an "Increase in Expression" is a reaction driven by the other person, aiming to establish or manipulate a connection.
To take another example, a normal girl, not reserved enough to be called introverted nor expansive enough to be called extroverted, will naturally behave normally with others. Even in a romantic relationship, the girl will initially behave normally with the other party; actions involving eye contact, hands, shoulders, lips, knees, etc., will not be activated. Only over time, as affection is gradually nurtured, will her volume of actions slowly increase. This is intimacy, which may include holding hands, stroking hair, or even kissing.
This is true not only in romantic relationships but in any relationship. Arthur in the police department acts extremely restrained, prioritizing work almost all the time. However, toward certain people he is closer to, he also performs more behaviors to interact with them.
Newborns are also a case like this, an unconscious "manipulation."
Because they are newly born, facing the harsh world outside, instinct causes the infant to unconsciously perform behaviors of closeness with the closest people—usually the parents—to self-protect. The most typical example is crying, which expresses weakness to elicit feelings of shelter, exchanging it for protection, food, and comfort. Of course, there are physical reasons to explain the child's behavior, but for a living and thinking organism, the psychological factor cannot be ignored.
That is why as they grow older, those intimate behaviors suddenly decline. The psychological explanation that adolescence is a rebellious period is not wrong, but it is not thorough enough. It must be said that the child's psyche and physique have closed off, no longer needing instinct to control "living dependent" on their parents. Furthermore, a significant portion of adolescents somehow unconsciously realize that they tried to "be close" to their parents through childhood behavior to gain living conditions, which leads to an inverse psychology: refusing connection with parents, rejecting dependency, and wanting independence.
In general, the infant is the clearest example of this mechanism, in its instinctive form. Its crying is a form of 'biological manipulation'—not in a negative sense, but a mechanism for preservation. It makes parents react with feelings of pity and care, thereby sustaining survival. That is why the older children get, the more these unconscious intimate behaviors decrease, as the instinct for self-defense transforms into the capacity for independence.
According to Erik Erikson, adolescence is the period of identity formation, as the individual gradually separates from dependency and moves toward independence. The "rebellion" people often talk about is actually the psychological manifestation of the process of detaching oneself from the old belief system—the parents.
Another case is also the unconscious manipulation mechanism of instinct to protect the subject, but in adults. After all, this is quite common in horror movies.
A person running from a killer happens to meet a passerby. This fleeing person will quickly approach with a cry of "Help me!", gripping the passerby's arm—a behavior a normal person would not do under normal circumstances if meeting a stranger, even when seeking help. Next, when talking, this person's face will be slightly upturned with their eyes, and this is also not a common communication method, but an unconscious self-abasement to persuade the opponent, in other words, a plea.
When people face danger, they automatically seek protection—even through extreme behaviors. A person being chased rushes to ask a stranger for help, grabs their arm, and looks up—that is not just a plea. It is a strategic self-abasement, a midbrain reflex aimed at activating empathy in the opponent.
In short, everything locks onto the Increase in Expression.
These two people just met for the first time, but the female student, in the short time she approached him, performed intimate behaviors such as sitting close, touching hands, and even leaning her head on his shoulder. Based on all the evidence mentioned above, Arthur can be certain that she is intentionally using intimacy to manipulate the male student.
Interpersonal behavior cannot escalate that quickly.
Upon hearing this, some might refute Arthur by saying, "What if she fell in love with him at first sight?" To this, Arthur would only smile faintly: sudden love only increases the speed of cultivating affection, like accelerating a car, but it doesn't switch from a car to a private jet.
The most essential core is the Increase in Expression, not the increase in affection. Like children in a family, they are nurtured by their parents from a young age, forming a very solid bond, but the practical behaviors expressing love are relatively few compared to the level of attachment it should have expressed. Therefore, this is just a means to evaluate a different aspect.