So most rating is pretty easy, it's just how many people rated it.
But most popular is strange. Somewhere i read that it's quite complex algorithm combining als kind of stuff. https://itch.io/t/20674/how-is-popularity-determined
I am not sure if popular on gamejams submussions is the same.
My submission sorted by "most popular" is constantly swapping. Before i started writing i was on the last 9th !!! place. Now i am in the middle.