Nah, you aren't going anywhere.
It's always hard to gauge feelings on these forums, but you can see you're taking the dog's death hard. It sucks, no getting around it. You feel bad for the old man, even though he accused you, because you know how he felt losing his friend. But that wasn't your fault. And even if it WOULD have been you that hit his mutt, it still wouldn't have been your fault. Who knows why the man's dog was out in the street? Most likely, the man was crushed seeing his dog, dead, and blamed the first person who came by. And that was you. Since he barely doesn't speak English, he's probably not even like many crappy Americans who see UPS, and look for a payday. He's just bummed.
You'll feel better. It just takes time. No one likes to see a dead pet. If you're an animal lover, it hits a deep nerve. I had to put down my lab last September, and buried him out back. It was one of my worst days. And you know what? When I'm working out in the garage, and I see the flower bed I buried him in, about half of the time that rat bastard still gets a tear out of me. But it gets better all of the time. Now, my wife went out and got a Chihuahua, and that makes me sad again. Not because it reminds me of my Lab, but because ITS A CHIHUAHUA!! That thing is not a dog, it's an abomination! But that's my cross to bear.
Only time will help. You probably know that. But you shouldn't blame yourself. You couldn't have done anything for the dog and the man.
As far as your manager, and his little space in hell, I would populate his paperwork with copious amounts of your own. I wouldn't let him get away with being such a lout. If it were me, I'd file a harassment grievance, and for the resolution, I would ask that he apologize in front of center. I would also call HR in Sandy Springs and run his name up the flagpole for creating a hostile work environment. Tell them you are "reviewing your options."
You just need to get to feeders, where you don't dread you drive into work anymore.