Well think about it from the Flatlander's perspective! They can't even perceive the cylindrical shape of their space. They wouldn't be able to go behind the cylinder from their perspective, all they could do is go forward far enough that the shape of space hides them.

It's not just semantics imo, cuz it would apply to us as well. If you're ever confronted with a 4th dimensional being then the only way you can hide is to get far enough away. You can't see the curvature of spacetime so that's useless for you.