That is not exactly how Zimmerman describe his behavior on his call to the police.
But there is nothing to back up Zimmerman’s description. If Martin was casing houses to potentially rob, I don’t think he’d be doing that in the gated community that his father lived in.
The most convincing explanation I’ve heard so far was by someone in a thread a couple of days ago who said that since Martin was talking on a bluetooth earpiece he probably would have looked strange to an outside observer. In his call to police Zimmerman mentioned that he thought Martin was on drugs, which is consistent with Martin seemingly talking to no one and gesturing with his hands.