Paph. armeniacum....probably a stress blooming which would account for the overall small size and the small pouch. The staminode shield is normal-sized; but, the rest of the flower should've enlarged considerably as the bud opened. However, flowers don't enlarge properly if the plant is weak, or stressed. So, that leaves you with a large, oversized (relatively speaking), staminode shield with the rest of the flower being undersized. So, perhaps armeniacum is also found in Vietnam; or the information given to you about it's origin is false.
Also of note: The colour is very faded compared to a normal armeniacum. That could be just a regional difference (if this plant is truly from Vietnam), or it also could be a sign of severe stress. I see this fading of colour in plants (foliage and flowers), that go too dry at some point during the later stages of bud development. So, with good culture, this plant could rebloom with a large, correctly proportional, deep yellow flower and clearly show itself to be a normal armeniacum. Time (and reblooming), will tell.....