What would initiate MariaDB to start to resolve IP addresses?

While it is possible to restrict access to the DBMS server using the firewall, it is better to not to make it accessible from the Internet in the first place. That way it would be most secure.

You tried it the correct way:

[mysqld]
bind-address = 127.0.0.1

It is strange it appeared unresponsible when connected using localhost. Instead, it should appear faster, because OS communicating via loopback interface hopefully avoids some layers in the network stack. This may mean some name resolution (e.g. DNS or hosts) problem on the machine. It is wise to avoid name resolution in this case, using the literal localhost IP address 127.0.0.1. Just specify it in the connector as the DBMS server address.

The last warning about the hostname "which resembles IPv4-address itself" is useless. The hostname is the result of the DNS query, and the value of the host name in the PTR record is completely controlled by the IP address owner. They can put anything into it, it can be made similar to the IP address itself, or similar to some other IP address (for greater confusion), or be a joke, or a poem line, or be rough and crude. It conveys no valid information for you to consider in the context of security. Just ignore this warning, or better yet, turn off such warnings entirely and don't waste resources on such silly comparisons.