yeah that issues happened on pokemon XD and colosseum and it was fixed for a very long time, it also happened on all controllers and not just wiiugc adapter even bt controllers, it was a game bug.I am absolutely positive that someone else had this exact issue with a GameCube controller. Does this happen in all games or only certain ones? Also what Nintendont version are you using? I think the issue was specific to Pokémon XD if I’m remembering correctly where the character would go opposite if the control stick was pushed to max. I believe it was eventually fixed.
But i never heard of this issues on any other game tbh and even those games were fixed like years ago, unless he has an extremely outdated nintendont and its using those 2 games.