Those "beaver tail" beer tabs are getting to be a real rarity, in his defense. If he'd found a whole chain mail vest made out of them he could have made himself a few hundred dollars on Youtube.
I enjoyed watching this, but I don't see how metal detector people in a public area are bad. They were civil with whomever questioned them and agreed to leave if that was the rule. In my opinion, it was two bucks and various trinkets fairly earned.
A long time ago I picked up a detector at a yard sale. I looked up my local ordinances about this kind of thing, and most public parks or other places don't care if you poke around and dig stuff up so long as you replace the grass and/or don't leave gaping holes for people to trip in.
I did find some WWII era metal toys near my house, which was kind of cool, but I don't make a habit of hauling the ol' detector out. Most of what you find is pull tabs and old nails/screws anyway. America has a deficit of Romans burying coins and stuff, making the hobby not quite as attractive as in, say, Britain.
Metal detector finds of Roman and Anglo-Saxon artifacts are revolutionizing ancient and medieval archaeology in Britain; several game-changing hoards have been found in just the last decade alone by amateur hobbyists.