I'm sorry this happened. There are dogs out there that are aggressive. People do keep them. People believe they can manage them and often they can. Sometimes they make a mistake and there is a terrible accident.
I don't know what to tell you. You can be walking your dog and lightning can strike you or your dog. Your own leash can break and your dog might dart out in the road and get killed. I guess what I would do is to count up all the days that I have walked my dog without anything bad happening, and then see what the odds are, how likely this is to happen again. Maybe I would carry a bat or a stick to try and ward off any other dogs. But sticks can make some dogs react. You can carry a bottle of citronella spray, or a small air horn. These stop dogs pretty effectively -- much better than a "No, No, No!!!"
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC