I can understand that you are feeling very shaken up and angry about this, and I hope you and your dogs recover quickly!
But I have to say that I agree with a lot of the comments here that it does seem like an unfortunate accident, rather than an irresponsible owner. There have been several threads recently about people who have had there dogs attacked, and they have all been along the lines of unmuzzled, completely out of control dogs, and the owners have at best done nothing, at worst blamed the victim. If this man is already muzzling his dogs, I would imagine this incident will make him even more vigilent - he at least expressed concern for your dogs, rather than just walking off, and was probably mortified that his dogs had behaved so badly, and with such an impact on a young pup.
This doesn't mean that you aren't entitled to feel aggreived for your dogs - I think you all need some time to relax and get over what must have been an awful experience.
Aaaww I was sad to hear of your bad experince.
I just think people should have their dogs on leads before they leave the confines of their garden, especially if you cant trust your dog not to run off if somthing interesting comes along...Ok so they were muzzled and that a good job but they should have been on leads.
Hope your doggys are ok 
The difficulty here is that they ran
out of their garden - ok, so the owner should have ensured the garden was secure, but he didn't take them out of the garden off lead.
