Ummm, why if he hasn't spoken to me in 2 weeks, did he do this?

My ex and I broke up 2 weeks ago, have not spoken at all. i have tried to contact him a few times, but i was walking through the front room of my house and saw his car drive by. He lives on the other side of the main road, my house is aways out of his way. It wasn't something to be concerend about, not stalking but a simple driveby. What does it mean?