They weren't harassing you. They kept talking to you for so long because you had the camera, and they seemed bothered by the fact that it was night (I dunno what time it was), and you didn't do that friendly chit-chat thing. Not everyone does that with cops, but plenty do (especially guys, it seems). I think they left you alone because you said you were autistic, actually. It might just be what cops in your area are like, but in my area if you had probed at a cop asking something like 'how can you loiter in your own neighborhood' they would get upset with your very quickly 
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After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true.
--Spock