Care to elaborate? This doesn't explain to anyone why it's an error.
It makes sense if you don't know the context that it's the Goomba king and that the Goomba's are chestnuts, which you'd assume the translators would.
I mean in the sense that some context was lost to players outside of Japan. The joke is that Luigi's Adventure is hilariously low stake when you see that he's talking about the Goomba King, the piss easy essentially tutorial boss from the first Paper Mario game. So they should have just had him called Goomba King, like he’s called in the English version of PM64. Chestnut King seemed like a weird oversight.