Looking at the pictures it looks like the passenger compartment in the Smart Car was fairly intact. I wonder if the driver had the seat belt on. An airbag doesn’t help much if the vehicle turns over or in a multiple collision(with a car then a pole).
That being said, both drivers are generally better of in a collision between two large cars than a collision between two small cars.
It’s the pace of velocity change...in a collision all the energy is transferred to the low mass vehicle, which will then change velocity very quickly - much quicker than a larger car.