Had to drop this amazing series due to terrible translations. I noticed you retranslated everything, so I'm taking my second pass through this manga.
Thank you very much for your diligent effort!
It was shown pretty early on that he went to Vietnam, arrow even pointed somewhere around Da Nang.
So yeah. That's definitely a "Nguyễn".
But yeah, you can see the author didn't really work with Vietnameses.
The chances of the surname being the same is so high, refering by name is pretty much a given.