cullen.ns.cloudflare.com has no CNAME records.
Question and response
Question
dig cullen.ns.cloudflare.com. NS
Answer
The response has no answer records.
Authority
cloudflare.com. 106 SOA ns3.cloudflare.com. dns.cloudflare.com. 2397556727 10000 2400 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0