Truly, I think it depends on the nature of the attack; what precipitated the outburst.
Was it a prey-killing, a scuffle over resources, was the poodle pesting the GSD, or did the GSD just go after the poodle when it was doing nothing whatsoever, and attack it? Without knowing the behavioral trigger, I wouldn't want to say whether the dog should be put down or not. If the poodle is gnerally antagonistic towards the GSD, then it would be most reasonable to find a new home for the poodle, IMO.
Either way, I think the owners are responsible. If one dog attacked and almost killed another dog, then I'd like to think a savy owner would not put the dogs in a situation where the incident could repeat itself.