That's terrible. I'm so sorry about what happened to your pup.
Wouldn't it be logical to the other owner to put his dog on a leash after it attacked someone once? I mean, come on...
As others suggested, try and get your pup to meet with your friends dogs that you know won't attack.
9/9/12 - Living like a king
Potty trained! Yay
Bang! (Play Dead)
Come (In progress!)