You say it is a busy road. You have to be sure you are not in danger, and not creating a dangerous situation, before you can reach out to help another. In the end, you had to go over a block and walk back. Anything could have happened, at any time, including while you were working on setting a foundation for a safe attempt to help the dog. So don't sweat the timing not at all.

Sure hope that doggie gets some help. I think the worst part is that you may never know what happens.