Without knowing the background of how the dog came to be off the lead, I won't pass judgement but yes most dog owners have had incidents where their dogs, often well behaved dogs, have behaved disgracefully. My dogs once shot off because SOMEONE ELSE'S child from the car next to mine in the car park opened the back hatch while I was getting a ticket. You never know why it came to be running free in the first place, so unless you're psychic I wouldn't be quite so judgmental if I were you.