Did I inadvertently unlock someone else's car doors?

I went out to get Bunny and I some lunch, and as I was leaving, as I used my fob to pop open the trunk to store the food for the trip home, I noticed that a car near my own honked briefly and flash its headlights. Odd, I thought. I then used my fob to unlock the car, and again, the nearby car honked briefly and flashed its headlights. I then used my fob to lock my car, but this time, the nearby car sat silent. I unlocked my car again, and again, the nearby car honked and flashed its lights.

I know that fobs have a decent range on them but I always thought the data sent was unique per fob. Maybe not? And then there's the fact that fobs can help criminals steal cars! That's more surprising.