Another Clio driver able to lock my 200!

So I was on a garage forecourt, filling up my Clio 200. There happened to be a ph2/mk2 Clio parked at the pump behind me. The driver of this other Clio finished fuelling and locked his car (his indicators flashed). As he locked his car, my car locked at the same time!

I had the key in my pocket, so no drama as I just unlocked it as normal. Incidentally, when I unlocked my car, this did not unlock his car.

Not sure if it is relevant, but I do not have keyless entry - just the normal remote control key.

Has anyone else had a similar experience?
 
That happens quite a lot. The frequency to lock a car will be shared by many cars. I seriously doubt he would have been able to unlock it though.