Hardly a scam, but it sounds to be to be a poor taste joke / urban legend type thing that a particular colour of bottle top is particularly required. I mean, why would it ? Are the beverage supplies going to try to ram the old ones back or to reuse them ?
Whilst I may be wrong I suspect you have found the best destination for your collection. As scrap metal it must be worth something, but it is a pain in the neck if you have to remove foil and labels instead of the recycler just burning it off or whatever.
Meanwhile maybe you can contact the radio station to ask who actually wants them and what use are they putting them to. You either nip another session of this in the bud, or miraculously find someone who has a genuine use for them. But I'd not hold my breath on the latter.