The exfiltrated data isn't for DNS resolvers but is leaked to Nameservers through them. A similar technique forms the basis of how services like dnsleaktest.co

The exfiltrated data isn't for DNS resolvers but is leaked to Nameservers through them. A similar technique forms the basis of how services like dnsleaktest.com and which.nameserve.rs identify DNS resolvers in-use by a particular client.