A funny experience I had recently

I had a very funny experience (atleast that's how I felt) a week back. I was on the side walk taking pictures of some beautiful flowers.

Picture of a lovely flower

I got tempted to take some pictures of moving vehicles as well. While I was taking some, all of a sudden from nowhere a Cop came with his lights on & questioned me on what pictures I was taking. I was surprised, but maintained my composure (as I did nothing wrong) & told him that I was experimenting with my new *ist DL. He checked my photos & left asking me not to take pictures of vehicles as it might cause suspicions. Any ideas on what that means? Do we have no freedom to take pictures on the street now?

Picture of moving vehicles