I don't see why you're giving this particular cop the benefit of the doubt when he's obviously shown he's a complete retard.
Because the evidence he's a complete retard only became apparent to me after I had written out my post.

How are you going to know if it was something three blocks away that happened 4 years ago?
Well I won't know, but his superiors will.

If you see someone sitting on a patio where there's a no trespassing sign, that alone is not very suspicious.
Agreed.

At that point the cop should have put 2+2 together and said 'have a nice day, sir' and fucked off. Instead he decided to go on a power trip and try to boss the guy around a bit.
I agree with this if the cop has no reason to be there.