I've always been told that the "certain number of hours" rule is just a myth. Probably they simply lied to your parents because they knew, or anyway suspected, that your parents were full of it.

And since they were right, great, all's well that ends well, but in principle I'm not really a fan of police making up their own rules or breaking the ones that actually exist. (Even if, really, an adolescent who is a few hours later coming home than expected is virtually always totally fine.)

It may have been better if they'd followed procedure and then came down on your parents for filing an obviously false report. Or anyway, I'd prefer that in principle.