Kate you made my day. Their are not too many people in this world who would have stopped what they were doing to make sure the stray dog ended up safe, not only that but you found the owners. You truely did a wonderful thing, THANK YOU..
BTW, I keep dog treats in my car at all times, along with a spare slip leash. Their was this one time when we were driving home for lunch and we seen two dogs running stray together, you could tell one was older and really tired but trying to keep up with the younger one. The younger one was barking and growling at us if we tried to approach him. But the poor old guy just wanted a nice warm place to rest, so I opened up our car door and he jumped right in and layed down. The younger one jumped right in after him and was fine from that point on.
You stayed calm, and proved to the dog that you weren't their to harm him, that was the best thing you could have done.