I think the words "UNLESS they have reasonable suspicion" are key, what is suspicion?  If a person is loitering by virtue of spending a considerable amount of time in the same area is that suspicious, whether taking photos or just standing around? I understand the point that is trying to be made, that the police have no right to ask what you are doing, and I believe that is a naive point to be making.

In today’s world if a person was in the same area for a considerable length of time I find that suspicious, the fact he/she has a camera is incidental. I think the police are just doing their job in a responsible manner to simply ask a person politely what their name is, I would certainly not be offended by that, however I found the behavior of the photographer rather suspicious myself.  Why not just say, I'm taking pictures with a new camera and my name is ______ and I live a few blocks away or am visiting this beautiful area, instead of asking, "are you detaining me".  

His constant asking if he was being detained was suspicious to me.  I don't think suspicious behavior is limited to covertly taking pictures. I have no doubt that had I responded the same way the photographer did I would have been locked up in a number of jails throughout the world.  Common sense and courtesy by any photographer goes a long way towards getting the picture you want verse being taken away.  Perhaps that is the difference between the amateur and professional.