What is the +3 next to the comment count?

I’ve seen this recently and have been wondering. My guess was that I’ve upvoted this user three other times but that’s probably way off.

8 comments

I think it means there have been 3 new comments either since your upvote or your last viewing of the post.
New comments since the last time you were in that thread
- That’s an awesome feature!
It’s new comments
- Thanks!
  
  No problem. Glad I could help!
I found this confusing (as did the op). Maybe instead of using the plus icon and making it stand out, it could just be 41 (3 new).
3 new comments?

You've viewed 8 comments.