I tried to connect FTP(i.e., with TLS/SSL disabled and Explicit choosed) with default file manager in Linux Mint(Nemo is the name of file manager I guess) it says "Permission Denied" with FTP anonymous type.As to the password being mandatory, this is not always the case for FTP servers which are capable of granting anonymous access with no credentials. That being said you bring up a good point. I'm just guessing but I think the admin account is just a placeholder which is functioning the the same way and anonymous account would.
It is not the case with previous MiXplorer versions(I use 6.56.5-API26).
But when I add password and use FTP login type, it worked. So it seems like password is mandatory(may be a bug(?))