It is NOT a sub-server. It is not a server. There is one server, not sub "servers". They are called SUBDOMAINS. not just with cpanel. That is what they are actually called.
How can I fix this problem and change it back to a subdomain like the rest of the internet?
Why did the devs make so many non-conventional names to make things 10x more confusing? I want everything to be named the correct names. Not "sub-server" and "virtual server" which is NOT WHAT IT IS. What you are calling "virtual server" (which indicates a VPS) is WRONG, it is a DOMAIN ACCOUNT and therefore should be called DOMAIN, i.e. "Add a Domain".