Sadly this is happening. And all it is about is to make people playing their games. I has written a post about this. You can see it here https://itch.io/jam/brackeys-8/topic/2341287/what-comments-and-posts-really-mean... . In your case they have not put a link to their comment, but they still uses most of what they write to make you go and play their game.
I was wondering the same. I had some comments on my game but sometimes I received comments without any download of the game in analytics...
And I saw on my dashboard game page that I had 0 ratings... could analytics be wrong ? :(
Edit : It seems that the ratings in the dasboard are not up to date since I can see a number of ratings in the submission page of my game. Weird.
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.
