http://www.youtube.com/watch?feature=player_detailpage&v=zcgbiNN3N44&t=47

I noticed in the video at 0:50 that the person is flying with throttle reversed, i.e. the engine idles when throttle stick is pushed forward.
Is there any particular reason for this?? Or just a matter of choice?

I think the guy is flying with Mode 1 transmitter hence the throttle stick is on the right. The odd thing that you have noticed is (throttle working reversed) is I think the guy personal preference and that is how he might have been trained. I do not see any particular reason for doing so or a reason why he can't change it to normal though the engine he is using is running is a unique looking and has an insane power and prop sound at the top end.

At the start of the video, it says that the engine is a self-made 3 cylinder engine

The video says engine is 192 cc, we have bikes here with less capacity.....