I had something similar happen yesterday.

I opened a thread about pokemon, browsed it for a bit, did some stuff in other tabs, and clicked back to the pokemon tab maybe an hour later to browse some more.

The post had changed to one where a user was asking for relaxing game recommendations and it was loading in new comments that seemed to be from that post, but I could still see the comments that had already loaded from the pokemon post when I scrolled down.

When I refreshed it changed back to the pokemon post and only showed comments from that.

Here’s what I could find on the api: There’s an API section1 of Lemmy documentation that describes some basic information and links to other resources. The LemmyHttp class in the linked lemmy-js-client documentation lists out the endpoints, parameters, and return values.