Did i see a possible dry run for a terrorist attack?

I swear, Eagle's Scout honor, that I am not making up this story. I have already called 911, but the woman who answered didn't seem to care much about what I had to say. I went to the Wal-Mart on North Prospect Avenue in Champaign, Illinois at approximately 10:10 PM this evening. I parked my car towards the back of the parking lot. As I was opening my door, this car parks next to me. They almost hit the door that I was opening so that caught my attention. After this, I start to walk towards the Wal-Mart entrance. I glance back, and see that two Arab males came out of this car. Both opened the back door of the car and put on backpacks. At this point I start to freak out, why would someone carry backpacks into Wal-Mart? I walk into the entrance and veer off to the left a bit to see these guys walk through. They walk in about 20 feet past the double entrance doors to Wal-mart, and then stop. They scan the store from left to right, don't say a word to each other, then turn around and walk out of Wal-Mart. Am i right to be freaking out here??? Why would they turn around like that, if not to judge how people would react if they walked into Walmart with backpacks on???