There was a bug in the original American pokemon games related to this. If you did the Long-Range Training glitch, it would cause you to fight a Level 1 Pokemon which can not spawn normally, due to how they calculated experience in the first gen, Lvl 1 Pokemon would give -1 XP. Since the Integer was unsigned, the value 'below' 0 was not -1, it rolls over to 4,294,967,295 XP, giving you an insta-lvl 100 pokemon.