Basically I made a post on blahaj and someone from kbin commented on it somehow even though we're not federated with them; I only happened to see the comment because I decided to look at how big the emojis looked to blahaj users so I went over to the same post on blahaj and there it was
Your post is on blahaj. kbin (or any federated instance) copied a version to their server so their users will see it in their "everything" feed. Kbin user comments on the post. kbin syncs that comment with all federated servers. Kbin isn't federated with hex so that comment doesn't get sent here and you won't see it on hex's copy of your post.
Ok thanks, that explains it <3