It's not clear that it's a coup, but some kind of nearly mutinous ... message.

The Army bombed a bunker this mercenary group was in, so they surrounded an army HQ building, and are now walking around in it """"making sure that the army isn't intentionally bombing them. """

I wouldn't call this a "coup", because Russia has had full scale coups in recent memory; including the August Coup which Putin was alive to see.