Cool. Too bad you didn't have a camera with you, you could've snapped a pic and maybe caught something on film.
Another possibility is the wind was blowing leaves in such a way that it sounded like footsteps. One night a few weeks ago we were outside in front of our house when I heard what sounded like someone walking or running down the street. I looked but didn't see anything. For a second I thought, "do we have a ghost on our street?", but it also sounded like a leaf skipping across the street in the breeze, which is probably what it was. But since it was dark, I couldn't see the leaf, but it definitely sounded like someone.