ns2.atom.com has no CNAME records.
Question and response
Question
dig ns2.atom.com. NS
Answer
The response has no answer records.
Authority
atom.com. 1668 SOA frank.ns.cloudflare.com. dns.cloudflare.com. 2397091647 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0