Points gain bug

A GM gained 25 points after winning this game: lichess.org/gH9VVd9u/black
he was 2992 and after winning 4 points he became 3021
Edit:
Now I realized that he may get that rating out of playing against a cheater but 25 points is huge, so I am waiting lichess to check if it is a bug or not

It's just because the GM has played 19 games and gained 21 points after that game you mentioned :p