was i out of line?

the subject of dog aggression and (poor) handler behavior has come up lately and i wonder if i was out of line today - can someone please clarify what the appropriate protocol is for how to handle repetitive humping? for example, we were at my usual park today and a dog was being mildly aggressive toward shaia - hackles raised, repeatedly lunging at her throat/dragging her around by the neck. not hurting her, but shaia was ineffectively trying to fight his dog off. she would end up on her back on the ground (she is very submissive) and when she would try to get up, he would hump her back down to the ground. she would get up and get away and he would come after her again, same deal. 99% of the time (well, 100% of the time up to this point) i stand back and let them work it out. after this went on for a while (shaia being humped to the ground) and the owner didn't intervene, i grabbed the dog's collar and said "enough" and dragged the dog off my dog. the owner then grabbed her dog and left. was i out of line? is it ok to intervene when someone else's dog is repeatedly humping your dog? shaia wasn't being hurt by this dog but was clearly uncomfortable, and more than anything else, i was really annoyed. i felt weird about it afterward though.