https://www.dnsinspect.com/mydomain.tld shows:

Allow Recursive Queries
WARNING: The following name servers announces themselves as open DNS servers:
On all name servers which acts as caching name servers recursive queries should be restricted to local networks. Having open DNS servers can lead to abuses such as cache poisoning and DOS (denial of service) attacks.
Check for Lame Name servers
WARNING: We found name servers which are not authoritative for your domain. Lame name servers:
All of your name server should be configured either as master or slave for your domain, if a NS records points to a name server that does not answer authoritatively, name server is called lame name server.
per the Linux command "whois mentionedIPv6", these IPv6 seems to belong to Cloudflare.

After asking my provider they have told me that it appears because i am using my own registered (custom) nameservers. These nameservers are registered at Namecheap and managed on Cloudflare.

And inside Cloudflare, DNS section i have found i have AAAA (IPv6) records for my nameservers set to mentioned IP. Apparently i have used this open DNS IP because i had no other, yet it seems to be bad idea right?

When i was checking the hostname of my hosting server i have found it seems not to be IPv6 ready: