Or am I underestimating how mainstream HN has become?
(of course there's still the possibility that these comments are actually genuine, however unlikely. In that case my apologies for making the wrong assumptions.)
Votes and comments for promotional reasons are against HN's rules and tend to get accounts and sites banned. We want people to participate because they find a story intellectually interesting, not because they or a friend have something to promote. It's totally fine to post your own stuff, but after that, the HN community needs to drive.
But then the underlying problem is that all these comments seem fake, which clearly indicates they don't offer any value and only hurt the product. So I'd say if you really love riddle.com, either just upvote the post, or add something meaningful to the conversation :-).