Or to Bethesda using Japan as a cultural anologue for Yokuda before they started leaning to the Middle-Eastern side. In fact, Gaiden Shinji was named in Arena, before Yokuda had even been thought up.
However...if you read all the stuff in Redguard pertaining to Yokuda and Yokudan culture you would notice a clearly Swahili-influenced culture (with some very small Japanese aspects).
The whole transition to Arabic/Persian culture seemed to have happened around Yokuda's sinking. Combine that with the fact that the Yokudans also developed a more elven religion at the time, combine it with the fact that a group of Yokudan elves were also killed off around that time by the Redguards and there seems to be some kind of event that can be extrapolated.