You are wrong, every user gets a merit airdrop when the merit system was implemented on the forum in January 2018. This airdrop merit is distributed based on the rank of each user, and the activity of the account mentioned is a hero considering the amount of merit airdrop.

It's okay to delete posts, maybe the user has a reason for doing so. About activity, the count will only be 0 if all those posts are deleted. Meanwhile, if the number of your posts is still more than the number of activities, then the activity will not decrease.