Notification Feed does not identify precisely who posted the new comment
When you subscribe to a thread with multiple participants and a single participant adds a reply, you get a notification.
But the title of the notification includes the name of everyone in the thread who have commented so far ("A and B replied to topic", "X and 2 others have replied", etc') rather than the most recent post which triggered the notification.
If there have been multiple comments since you last visited the thread, it's fine to "roll-up" all the comments into a single notification, but if there's only been one comment it's less useful. You might as well just write "a new comment was added to the thread", without naming anyone. This behavior doesn't occur in "Recent notifications" - it just tells you who posted like it should. This looks like a (small) bug to me.