Street Dogs Only Interested in Other Dogs

This time-lapse video I made of a Thai street dog taking it easy has an interesting ending where a bark triggers it to jump up and run across the road with all its friends. But what triggers the bark? There's a lot of activity in this area, which is a university, with traffic and pedestrians continually passing, however the dogs ignore all this. They even ignore me, a total stranger, sitting next to them to take a video.

Then a man with a pet dog walks passed and all hell breaks loose. This, I believe illustrates the big difference between street dogs and pet dogs: pets are socialized to people so react to strange people as they do to strange dogs which often means confront them, but most street dogs are not socialized to people so ignore people unless they have food or look like a physical threat. 

Hence, these street dogs ignore me (a human stranger) but challenge a pet dog (a canine stranger).