That is so terrible, I feel just awful for him.
I can't say I would let knowing that a dog can attack another dog stop me from taking my furkids to the park or on walks though. I am always overly cautious, and after many incidents at the park w/off leash dogs now carry HALT just in case. But the dogs love being outside and to run and smell new things at the park, so I just continue to be as safe as possible and take all the precautions I can.