When users filter their Inbox to “@mentioned”, they still see notifications for comments and task activity where they were not explicitly @mentioned. I believe this happens because they were @mentioned in the past—even though the current comment or update doesn’t reference them directly.
Makes (some) sense: Folks don’t always remember to @mention someone, so the filter is designed to help users avoid missing messages that are effectively “for them.”
Since this behavior is intentional, the gap is around expectations. If "the @mentioned filter can’t strictly represent explicit @mentions**, it would be helpful to offer a separate filter that does.**
This feature doesn’t resolve this: Introducing filters for Inbox 
- News / Product Updates - Asana Forum
See Question about the @mentioned Inbox filter — am I misunderstanding this?