I had the same positive experience already twice this year on HEL-JFK and HEL-PEK. Both flights were only about 50% full and I was sitting in 3A and 2L so I don't think they would have run out of my choice even without asking. But it sure was a nice gesture anyway. I didn't see the purser asking anyone else the same question though so maybe the good looks helped in my case too... :P