The " Panning" Shot

I was in a taxi home from work. It was too cold to go out to take pictures as I was wearing high-heels and really thin stockings. I was looking for something to take a picture of but I had a feeling I wouldn't get anything good tonight so I just took a picture of a random taxi on the road without hope.
But the thing about this picture is, I was in a moving taxi and taking pictures of another moving taxi. So taxi was supposed to come out clear while the wall should be blury. It's so strange that it turned out the opposite. Kevin said this is called panning as I don't know much about how to take pictures professionally. But I don't know what I did to make the picture look like this. Seems like I've done a better job than I thought accidently.