Thank you Ken.
The documentation I was referring to was from:
where it says:
class UserCreationForm¶
A ModelForm for creating a new user.
It has three fields: username (from the user model), password1, and password2. It verifies that password1 and password2 match, validates the password using validate_password(), and sets the user’s password using set_password().
I will read up on the distinction between form fields and model fields. I am obviously confused on this.