Siz User nomli model yozgansiz, ammo djangoning o'zida ham shunday nomli model bor.
Hozir user login qilganda siz yaratgan model objecti sifatida emas , djangoning defaul User modeli objecti sifatida kirayapti.
Sizda (kamida) 2 ta variant bor:

1. Modelingizga boshqa nom berish(masalan, Profile) va uni one to one relationship orqali default User modeliga bog'lab qo'yish.

2. Custom User model yozish. Bu nisbatan qiyinroq, ammo siz kutgan natijani beradi.