Apex domains cannot have CNAME records.
Question and response
Question
dig wistia.com. NS
Answer
wistia.com. 5 NS ns-55.awsdns-06.com.
wistia.com. 5 NS ns-1706.awsdns-21.co.uk.
wistia.com. 5 NS ns-1446.awsdns-52.org.
wistia.com. 5 NS ns-792.awsdns-35.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0