I'm with Don and TB.
It is falsetto. I spent most of my middle and high school years in choir, and in high school I could do this with no effort. (and yes, I mean after my voice had already changed). I was booked as an alto my freshman year, presumably because gool 'ol Mr Hoover was short on altos, and because I could. :)
I'm very sad to have lost even my basic singing ability at such a young-old age, but my opinion is this is no big deal and no cause at all for amazment.