Gilly's dog possibly should have been on a lead, but that doesn't discount the fact that a large (by the sounds of it) dog with potential issues regarding it's behaviour with other dogs (and by extension) possibly humans wasn't muzzled, and the owner even with a lead lacked control of it.
A lead isn't the be all and end all of proper control of an animal, especially where it's a large animal and the owner (by the sounds of it) wasn't paying attention or willing to actually attempt control of the animal.
A lead won't even allow a lot of people to (easily) pull back many breeds of dog (and if Gillys' dog was on a lead and the other dog attacked it, there is no guarantee that the other dog wouldn't keep going after his dog/mum).
Our dog is a (fairly thick

) toy poodle, and yes he's always on a lead (mainly for his protection), but we also put a muzzle on him at times if we think there is any chance he might try and bite, which means he gets it put on outside the vets

(I would trust him with most children, but he gets freaked out going into the vets).