That was me that typed that bit up because a few users didn't know their FTP details after migrating.
Is asking for a website name for your hosting so myexamplewebsite would create myexamplewebsite.000webhostapp.com
The password is indeed the FTP password
So when you use FileZilla both the username myexamplewebsite and the password setup there will be used to connect to files.000webhost.com
Although they can use anything they want I thought it was easier to call it FTP username/password because most likely most users will then go onto add either a purchased premium domain theirsite.com, a free domain theirsite.ml, a free provided subdomain they can choose the full name theirwebsite.comeze.com etc.
At the moment you add your website to your account by naming it and it will create yoursite.000webhostapp.com if you tried to put in Geoffrey.com into that box it will probably create Geofferycom.000webhostapp.com and then you hit set web address and add your premium domain Geoffrey.com and link it to your account Geofferycom.000webhostapp.com
I hope this isn't too confusing I try to stay basic but sometimes stray