I think you did things pretty well. It was wise to leave when you did. I might have left as soon as I saw the off leash dog, but then again, you can’t always protect your dog from everything, at least in my opinion. Besides, that dog may have been perfectly well behaved. Turns out he wasn’t, and now you know that your gut was correct. I also think you made a good choice in letting your dog off leash as well. Leashes can cause even more issues and frustration.
Nothing horrible happened, and in my opinion, you handled it just fine. Please try not to stress over it. Your boy sounds like he got over it right away!
Forrest - GSD 9/1/2016 - 5/14/2017 RIP
Brooklyn - Golden retriever 1/30/11