it probably still works as a lightning address, but for it to be a "zappable" address is has to be able to create and publish the "zap receipt" event https://github.com/nostr-protocol/nips/blob/master/57.md#appendix-e-zap-receipt-event

The "allowsNostr" field is a way for the LNURL server to let clients know that it can publish zap receipts