If a post belongs to a community, comments will be muted according to the communities' rules regardless if you comment on it from their blog or from the community.

This is already true today btw: @hive-140075/test-s2fe8p

In this community I set @howo-test2 to the muted role, and then commented on the post from the account's blog, and the post ended up muted. If you want to test by yourself I set you as muted on that community :)