First, I can't speak to the laws of Maine but in some states you are allowed to open carry on your own private property.
Secondly, I agree in that the police only received a call stating there was an individual with a gun. Whether that is true or not, they will respond accordingly, as they did. As you stated, he wasn't charged and he's not even cuffed in the photograph so I don't see what all the fuss is about; but considering the news this morning reported about some kid who didn't get a foul ball at a baseball game, I can only guess it was a slow news day!
Lastly, the tattoo is not against the laws, unless we're talking about the laws of good taste! But one look at that guy and I would say he has a history of bad choices. Even the look on the deputy's face tells he's also thinking what a douchebag this guy is!
Cheers! M2