The point is, it is a full EV. The "hydrogen fuel cell" thing is a type of a battery. A lot of people somehow misses this, and thinks it of an EV-ICE hybrid. It's not.

The FC is a magic non-moving fin stack that generates electricity proportional to the amount of H2 and O2 fed through it. It's a type of a primary(non-reusable) battery. Nominal cell voltage is 3.7V and pack voltage is 370V for Mirai.

Not that it makes the car great, but it is literally an EV.