I believe the activity log is supposed to show all comments/replies, but it remains unfinished. This thread could possibly warrant being pinned, but has some overlap with Dawn of the Phantasms (nobody has solved it), and an ideal piecemaker thread will also have all the relevant links. Once one is made and pinned, one of those relevant links could be this one as well, for reference, but you are right in thinking something is amiss with the way that activity is displayed - it is honestly kinda broken atm.