Well, not to get off track on
that particular exact OP example (because yes it might have factors to merit what you're saying). But just "in general": What your saying, to deduce rules by asking someone "is metal detecting ok here?", would be a valid. And time-saving, I might add !

Because in theory: Whomever you're asking afterall, is going to tell what the law says (if anything) on that issue, right ? However,
in actual practice, it doesn't sometimes work out that way. Rather than tell you "here's what the law says", you can get odd-ball answers that make you ..... shall we say .... wonder.
Some persons have posted that the way around this "whimsical arbitrary" thing, is to phrase the question in this way:
"Are there any laws or rules addressing or forbidding metal detectors?". Because in THAT way, it puts the burden on them to CITE such an actual rule or law, if one existed. Right ? Rather than sounding like you're asking their permission, right ? What's your take on that TH'r ?