These five soldiers in black armor, riding two-horned warhorses, were clearly here for those thieves. But the eagle flying overhead gave away the situation, which let those thieves escape just now.
Ethan had [Cave Treasure Intel] on him. Once he used it, he could get the exact location of the treasure.
As long as he reached the spot and made a little noise, he could lure the thieves in the cave out.
They wouldn't just watch someone take their treasure and do nothing, right?
Ethan thought it through. He could totally use—no, help—these five soldiers find the thieves hiding in the Frost Valley cave.
Then, after they had mostly cleared the thieves inside, he could move quietly and take the treasure with almost no effort.
But before that, Ethan needed to learn how strong the cave thieves were, and how strong these five soldiers were.
If he followed the plan, went into the cave, and it turned out the five soldiers weren't a match for the thieves, that would be way too dumb.