Apex domains cannot have CNAME records.
Question and response
Question
dig auto.dnssmarthost.net. NS
Answer
auto.dnssmarthost.net. 5 NS ns2.siteground.net.
auto.dnssmarthost.net. 5 NS ns1.siteground.net.
Authority
The response has no authority records.
Additional
ns1.siteground.net. 5 A 75.2.77.104
ns2.siteground.net. 5 A 99.83.229.113
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0