Someone was taking pictures of my home- should I be concerned?

My boyfriend was waking by our front door and noticed a car parked in the middle of the road, taking pictures of our home. When he opened the door to go ask them what they were doing, they drove off. He said the driver was an older man and there was a passenger he couldn't see from the house. He said the car was older and not very well kept, but the camera was a big, expensive looking Nikon. I'm not sure if I should be alarmed. We have owned our house for over a year now. It is a fairly small house, with little aesthetic value. We also in a small town (6,000 people) and our neighborhood is on the less nice side of the town. There are a few abandoned homes nearby. I can't think of a reason anyone would want to take pictures of our home. There should be no reason to take pictures for appraisal, and it isn't much to see (very plain, no decor, and the yard is is muddy and slushy with the weather.) I know it isn't illegal to take pictures of someone's house, but should I be concerned about this? We drove around after and did not see any similar cars taking pictures of any other homes. Thank you in advance for your answers.

Read more: Someone was taking pictures of my home- should I be concerned?