Hi,
The description on the jam page is as below.
You need at least 10 ratings to be considered for winning. If there are less than twenty independent submissions, we reserve right to decrease the number of winners.
So, the number of ratings you need is 10. The twenty independent submissions above meant twenty submitted games, not the ratings. We apologize for the confusion.
Also, please note that the rating is public, i.e., anyone with an itch.io account can participate. You do not have to have a game submitted to rate.
Please let us know if you have any questions or further clarifications. Thank you!