In nostr every reply have tags of previous replies, so if you ask relay for replies of specific post, you are not getting just the main level replies but also replies of replies.

It’s a matter of grouping and how to show them/filter them locally and thats what i said, we have to improve our app in this area.

It’s same with downloading thread, if you want to get whole chain of post, they are usually included on tags on the main post. In some cases they are not (bugs etc) and we need to better handle those cases, cause it’s sometimes not downloading whole thread (pretty commong bug across multiple clients)