... the simple fact is there is no way to get fat without overeating.
Again, word choice... It should be "in general," not "simple fact." Why? There is a way to get fat without "over eating." If you know how to turn on survival mode and that would significantly reduce your body metabolism. As a result, you will gain weight even though you eat food less than the amount your body normally need.
Uh, no. You just moved the goal posts. If you "turn on survival mode" (whatever that means), and continue to eat the same amount, then you are now overeating. You can't gain body mass without inserting that mass into your body in the first place.