Mike mike mike .... I think you are opening a can-of-worms

I have no doubt he can show you something that says "you can't dig" or "you can't remove things from a public park or beach", etc... But do you really think those things were meant to stop a kid from digging a sand castle? Do you really think they mean your 10-yr. old daughter is in trouble for picking up a seashell for her grade school art project? Do you really think those things were meant to mean you can't metal detect (which requires, gasp, digging, and, gasp taking an item). No. Of course not. In fact, the laws predate metal detectors and were originally for things like:
Taking park features like the park benches, or backing up your truck and harvesting the sand for commercial purposes, or cutting down the trees for firewood, etc...
And as you have seen, a fellow ranger isn't so silly as to apply those things to metal detecting. But by your asking "barney-fife" for proof, sure, I have no doubt he can send it to you. And given enough semantics, sure, can apply to metal detecting, if you stand on one foot and squint at the wording real hard.
I'm glad you didn't have the the name of the other officer, lest this new officer merely "appraise him" of the evil of detecting. Or now goes about putting out a B.O.L. to all the other rank and file to boot md'rs, etc... (may happen now).
If it were me, and I got a "yes", I would stay as distant as possible from anyone who interprets differently than that. I mean, sure, if you were faced with a ticket, your other person's say-so would have to surface.
But then on the other hand, I don't like barney-fife's any more than you do. So perhaps I too would have done the same thing, to show him the silly-ness of the his statements. Unfortunately, you can see where front-&-center attention puts us

Therefore, when I've gotten booted (or as in this case, told "no metal detecting"), I hate to say it but: sometimes it means "avoid that one individual". If no one *really* cares except that one person, then presto, avoid that one individual. Sure it means having to detect at lower traffic times, etc... but ... oh well.