1) ALL owners are responsible for their own animal/s, be it on private or public land, & be it on or off a lead
2) In the scenario you describe.... On lead owner should have a muzzle on the dog (just owners opinion that their dog bit out of fear).... The attack on other dog *may* be mitigated by that owner not having thier dog on a lead, PROVIDING, that they were in an area that the law sates they must be on lead