I do think ambiguity is the main element that converts a documentary photograph into a street photograph, but I know there are a lot of people who don't make a distinction, in other words who feel that a documentary shot made on the street is street photography. At that point all I can do is suggest you can't understand the distinction without having studied the great street photographers. And, as usual, I always come back to the difference between HCB's street photography and his photojournalism. It's a fine line, and a subjective line, and I know there are many who disagree with me, but I'll stick with my definition even though I don't always agree with myself. I've included an example. Is this picture ambiguous enough to be called a street shot? I think so but I can see reasonable arguments against the idea. In the end I come down to Justice Potter Stewart's approach to pornography: "It's hard to define, but I know it when I see it."
Maybe it doesn't matter, but if you surrender the point then practically anything shot on the street can be called street photography. Not long ago there was a forum that claimed to be a street forum but that defined street as anything on the street or in an urban setting. The stuff that got posted mostly was either pathetic or hilarious. When that became clear, instead of changing their definition they changed their name.
Didn't notice the woman in front of the guy behind the tree. Now I see her. I don't think she detracts from the ambiguity enough to make the picture straight documentation. As far as the black gal among the sea of white faces is concerned: First, I can't be sure those are all white faces. Looks as if there might be a darker kid in the background. Second, integration has succeeded in the United States so completely that a black face in a white crowd or a white face in a black crowd doesn't look unusual to me. Fifty years ago it might have.