Anyone else have this happen?

He does this often.  He is in the garage along the driveway.  I drive in. He stands with his back to me - not acknowledging that I have come home.   Not saying hello and I KNOW he knows I am there.  Like at night when the lights are shining on his back or when I am right next to him with the car running.  What is that about? Is this ADHD related or is he just acting like a jerk?