ns2139.dns.dyn.com has no CNAME records.
Question and response
Question
dig ns2139.dns.dyn.com. NS
Answer
The response has no answer records.
Authority
dyn.com. 291 SOA ns1.p201.dns.oraclecloud.net. hostmaster.dyn.com. 4038 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0