Hi Tan, nice plant
Well, N. kampotiana also has round pitchers and it grows in southern Vietnam. It's much more common in cultivation and of course it's sold as "thorelii". But it's glabrous, while N. thorelii is hairy. At the bottom of this page you can find a table to distinguish all the Indochinese species:
http://www.carnivorousplants.it/desc.holdenii.pdf
If your plant is hairy, congratulations, it's probably one of the poached plants that has been put for sale in your Country. Actually, even if it's kampotiana, I can see a massive rootstock at the base of your plant, and that makes me think that it has been poached from the wild anyway...