What I understand the idea is to ask you to enter [email protected] in the username, and your lemmy.world password.
What I understand is happening (from the comment, because I don’t use apps) is that the app first expects you to choose lemmy.world in a list, and then asks you about your name and password.
Honestly, I have no idea what is easier for anybody. Both seem very equivalent to me. Also equivalent would be asking the server, username and password on the same screen.