Even in 2022, I don't expect scholarly level research for an RPG book. Although it's certainly nice when the author has that level of knowledge.
While doing some research for a class in college, I ordered a book via ILL on medieval currency, which was sent from Lake Geneva Public Library, with EG Gygax in the checkout list on the pocket, due back in early 1973... the price list in shillings is the D&D OE price list in GP...
On the page prior it mentioned that the gold penny (1 dwt of "coin-gold") was worth 10 to 20 silver pennies (1 dwt of coin-silver), depending upon debasement of each.
For reference, coin-gold was often debased with copper and a bit of silver, to about 12 d worth.
So Gygax did research... just not wide nor careful research.
other fun WTF? bits...
shujenka is a corruption of shugenja those who practice shugendō. Shugendō (修験道) Practitioners are called Shugenja (修験者) or Yamabushi (山伏)
I'll note that AD&D OA as released seemed way more Japanese than Chinese, save for the monsters; I expect wu jen to be a corruption of ___ jin.
(D&D 3.X OA is absolutely more Japanese than Chinese, due to also being a port of L5R's setting.)