I asked him what he wanted and he replied he was just looking around. I told him that this was impolite and not to come here again and walk around as if he owned the place.

You did the correct and right thing. Often times it is not just "looking around", it is snooping for ideas and "spying". You are damn right he was impolite!! Sadly, in the eyes of some locals, us being here and drinking water here seems worthy of curiosity:(