Snowballs

Yesterday the weather warmed up, and after Sam and I got home there was still enough daylight to be outside.  We stayed in the front of the house, where the sidewalk had been cleared, since he didn't have his boots on.  The melting snow was the perfect consistency for making snow balls, so I showed him how to make and toss them.  He was delighted with this new thing to throw.  We threw them on the sidewalk, at the fence, I tossed one at his belly, and we threw them high into the air to watch them "fall down!!"
Then a car drove by. He looked up at me mischievously, "I throw snowball car!" and pulled back his arm.
I cannot understand where that connection even came from!  Another innate "boy" thing... I swear that never would have crossed my mind!