"Trap" here usually means a feminine cross-dressing guy that tricks you into thinking he's a girl, hence you fall for the "trap" if you don't realize it. In this case though, it appears to be the standard meaning of the word, where the trap is being eaten by the treasure chest monster that seems to be using the shape of a girl as bait.
am i the only one who sees a potentialy fatal flaw in the form that this mimic has taken?
I mean, it doesnt seem to have any eyes facing the back, and someone could sneak up on it, force the lid part down, and cause serious damage or even sever the humanoid looking part with the teeth on the treasure chest part.