i reckon they followed it up because he is known to them , nutjob hardman wanabees with renegade children usually are.I'm just gobsmacked the police actually followed it up and gave him a talking to!
Anyway, as others have said, just forget it. The guy is obviously a bit of a nut-job and you did nothing wrong. I worked in customer service for a few years and had many a complete nutter go off on me like that. First time it bothered me a lot.........after a while I learned to shrug it off. Some people have issues - it's their problem, not yours.
just ignore him OP , ignore the calls too if they do happen , then get a block put on , phoning back and rising to it just encourages kids.