Those are wide area service discovery requests for the legacy browsing domain.
Usually, I would expect clients to have picked that up via your DHCP server's domain name option already.
From your debug log, it would seem that your DHCP server wouldn't offer a respective option.
Can you check whether your router would define (or allow you to define) a local domain name?
If that's missing, that could be an explanation why certain (Apple?/iOS?/mDNS?) clients would try to request that via a DNS-SD record from your DNS server.
However, NXDOMAIN is a valid answer.
It would have told the requesting client that there is indeed no local domain, and I'd have expected that client to stop its wide-area DNS-SD requests.
This seems more like an issue that should be addressed on the client side.