It sounds to me that it wouldn't go onto the building hex ... not being, as you mention, a low risk move, and it being a vehicle.
I'd take it as not being able to perform the order, and move down to the next order on the card.
I think you're right. I played it the same way as OP though and it makes this scenario very tricky I think. The German is defending so a defensively driven half track makes sense and is tough to destroy.
I think interpretation is successful with this scenario, but I think yours is right.