And they don't play with any friends what so ever? Note that I'm not trying to out you, I'm simply trying to be 100% sure that there was no outside bias that had anything to do with your kids behaviour. Add to that that we don't know how you our your wife treated your kids, the study from the kindergarten that I wrote about was real and not made up so even though you might think that you behaved exactly the same when your girl played with dolls/cars as you did with the boy, there is a slight chance that you didn't and even didn't know it.
On the other hand there might not have been any outside bias what so ever and it just so happened that your boy preferred the car and your girl not. One cannot draw conclusions from a "study" with only two participants
And why you bring in the battle scene is beyond me, didn't I write that men and women where different? It's just quite difficult to have a genetic bias towards a toy car in a species that evolved long before there where any cars and when the porpose of the car is not apparent for the child.
Once you are grown up and really try to drive a car there might be a male bias towards driving due to the speed or what not, but that is not something that a small child have any idea of what so ever!