Apex domains cannot have CNAME records.
Question and response
Question
dig sbl.avpms.hu. NS
Answer
sbl.avpms.hu. 4 NS ns2.loom.hu.
sbl.avpms.hu. 4 NS ns.loom.hu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0