After that day's conversation with Wang Linchi, the Exam Ghost disappeared. He claimed he wanted Linchi to return to the Righteous Path of 'studying', but it was all probably a pack of lies. After all, he was afraid that Linchi might turn on him. The idea of being turned into a ghost sigil didn't sit well with him either. He had probably just guessed it, accidentally let it slip, and then had to deceive Linchi as a last resort. That's why he escaped afterwards.