Well either the link is definitely being opened before or your instance is glitching and thinks it has. What you’re describing is the new comment feature.

Normally it works by you going to a link for the first time and it loads all the comments. You can add comments and they’ll show up as normal but when you refresh the page or revisit it highlights all the stuff added. Your comments fit that criteria as they were added since the last time you visited it.

Wouldn’t be surprised if there was a lemmy glitch over it. Something to ask your instance admins about for sure.