Are you sure on the size? It can be hard to tell from pictures but it looks like a 16" to me, GTs are measured centre BB to centre top tube up the seat tube. I have an 18" and it actually measures over 20" to the top of the seat tube.
You certainly got a bargain, I didn't think anyone would ever beat the $500 I paid for my frame and 2 pairs of XTR V-brakes, but at current exchange rates you may have the cheapest Xizang ever!