I think the OP's HLE ran out of cars and only had that to give them, regardless of class booked. I could see the Yaris sedan as a B-class, which I think it is, but the hatchback is a stretch in B, let alone C. I recall reading somewhere in this forum about a poster who was given a Rio as midsize. The poster then asked to be shown examples of two cars smaller than the Rio (compact and subcompact), and was promptly swapped into a proper midsize car.

Wouldn't help in the OP's situation, but might be worth a try at a populated airport should it occur again. Nothing makes me grin more than watching an ill-conceived policy fall apart when a defence is attempted.