Sam,

What you may find is that due to the most recent rash of police shootings around the country, they are on much more hightened alert. Some of the shootings have been ambushes and for a cop, the people who they feel are sneaking up on them, are going to bring on more suspicion. Even though you felt you were doing no wrong, they didn't know that.
Since there has been a lot of lawsuits over the past few years, the chances are you are on video camera. So if there is abuse, it will show that. If there was not, it will show that also.
You might have fit a description of a suspect in the area. They would have to handcuff you to make sure you couldn't get away until they verify your identity. If they did not do that and a suspect escaped and hurt or killed someone else, they could be held liable.
A few years ago I was pulled over in the state of South Carolina, for no reason as well. I drove a very nice car. They were looking for people smuggling drugs and guns in and out of the state. I let them search my car, and was on the road in 15 minutes. No big deal.
It is sad that we sometimes have to deal with harrasments. Taking shoes off at the airport, etc. But that is part of the price of living in this society. The fact is I would rather have a personal inconvinience now and then than the other side which is no laws, lax laws, acts of violence, and terrorisim and total chaos. I hope your case turns out to be nothing. It might have been just a random search and nothing much will come of it. Good luck to you and stay away from cop cars.

MAB