Hi Nickman87,
I believe it's participant voting, apparently we got over 3000 ratings last year on 104 games (I think there were 800 participants). I rated ~30 games myself.
https://itch.io/jam/gamedevtv-game-jam-2021/results
Edit: just to say there was a lot of mutual feedback (detailed comments) and reviewing which was definitely one of the highlights of the gamejam experience!