After almost 8 hours of looking into every possible theme file and googling around, I found the markup responsible for activity comments – I thought I would share the info in case someone else will be looking for it in the future.
Turns out it’s nowhere in the theme files, but in BuddyPress files in buddypress/bp-activity/bp-activity-templatetags.php file. The function `bp_activity_comments` is defined around line 633 and it has a comment that this solution is temporary:
`/* TODO: The HTML in this function is temporary and will be moved to the template in a future version. */`
It can be edited there, but I’m assuming it will be possible to do this in theme files in some future version.