Oh, how awful...I am not at all a cat person, and that's just one reason why.
A few things: First, I sure hope the cat wasn't feral. Actually even if he was an outside house cat, if it drew blood then always think: Infection. Recall how they bury their feces and urine with those paws. Call the vet.
Second, if it was an outside cat and your puppers was on lead, consider ringing the bell and informing the owner. In much the same way that we wouldn't tolerate this from a dog, same for a cat. Responsible pet ownership, +1. Especially if there's injury and a vet bill.
Third, stay away from the scene. Yes, you could work him thru it, and offer treats...but unless he has some generalized symptoms, then the best course of action is to just avoid that spot. If he has a more generalized anxiety reaction...doubtful, btw...then that's a different story and a different response. But for now, just avoid the scene and let it fade. At a year, their attention span is about 4 minutes, anyways. Going back and trying to work thru it might keep it around much longer.