When an attachment is added to a task, it automatically creates a comment. This seems redundant and creates a lot of spam in the Comments section, when it could only appear in the All activity section.
That’s a way to inform everyone an attachment was added, and look back at the order in which it happened + what were the discussions before and after. In a complex discussions with lots of comments, it seems necessary.
It should be an opt-out setting. With many attachments added, the discussion actually becomes harder to navigate.
I believe it was recently introduced at the project level with a new column 
do you see it in “member’s notifications”?