This is what it says:
"Voting will open shortly after the jam ends and is open to everyone who’s submitted a game. Entries will be rated on the following categories: Overall, Gameplay, Graphics, Audio, Innovation and Theme Interpretation. Voting will end on TBD.
As always, we'll highlight some of our favorites games on the GitHub Blog, and the world will get to enjoy (and maybe even contribute to or learn from) your creations."
My guess is that they will play the most popular ones and/or the better rated.