It’s because he has a new account, and new accounts gain and lose much more rating than normal players so they can get to their real skill level faster
I assume it’s your game against “classyear”, you might say he doesn’t have a new account but it’s because he’s new to specifically rapid, and has only played 6 games and only 2 in the last year.
I lost a rapid game, and the strange thing was that my opponent's rating increased by 208