Wrong. The patently irresponsible dog owner was exactly that: Irresponsible. If he had a habit of digging holes and/or escaping, which he clearly did (though let me guess, this was the first time he ever did it, amirite?), your uncle should have either reinforced the area, trained and disciplined him better, or put him on a leash.
Your uncle was at fault. Your uncle is the one who was in the wrong. It is not a motorist's duty to stop and track down any potential owner of some random stray dog -- which is exactly what it was if it had escaped, and for all the driver knew it was feral to boot -- that runs out in front of their car. At most, some jurisdictions might have a (totally unenforced) bylaw that requires you to call the cops or animal control, but that's about it, and most people are completely unaware of that regardless.
As much of a dog lover as I am, dogs are not humans, so the twits trying to associate this with a child running out into the street (in which case it would still be the parents fault 99% of the time) is absolutely ridiculous beyond belief. There's no comparison to be had there, either ethically or legally.
Quit fucking blaming other people for you (sorry, your uncle's) shortcomings. There's no one to blame here except you/him. And whining about it on a fucking MMO message forum is even more stupid than this whole discussion is.