To answer your concerns:
1) Yes, a lot of people (~30-60%) spam-comment. You can often find this out by going to commenters' profile and see times/intervals at which they post comments. Some people comment on different games as often as every 1-3 minutes, which obviously means they haven't played
2) There are two types of ratings: game rating (general ones - a single 1-5 star) and jam ratings (jam specific - several categories, 1-5 star each). Your analytics page likely shows general Itch rating.