We have the benefit of looking at a picture and taking time to try and decide is it an air rifle, pellet gun, rimfire etc. Imagine if you walked up on this picture and he raised it towards you. A split second decision that will be life changing for both parties. Don’t trespass and if you do you better not have a gun of any type.
Quick look and guess it's an air rifle. He looks like a decent kid, pants aren't saggin' and no wide brimmed hat cocked sideways. If he's trespassing, I'd approach and ask him to not do that.