>>49389859It honestly doesn't make much sense in context either. The guy threw the Medicham into the volcano because he was kinda on the bad guy's side, but then the bad guys(with the Garchomp) proceeded to kill his teacher because what else is he going to do after she's defenseless and has no pokemon, and then he just kind of switches sides.
This will happen regardless of if you beat the bad guy's over leveled Garchomp too.