Yes, I read the article. We only have the parents word that she's not over weight. They could be in denial.
What, so we should take your word for it over theirs? That seems entirely reasonable.
Anyway, The BMI is at fault here, not the Wii. That's my point.
Wait, so the parents were in denial about how heavy she was, which would make the BMI result actually correct, not at fault. Unless they weren't in denial (more likely), and they gave the correct figures, which, if you bother to check them against the BMI, show that she is normal and healthy. Either way, the BMI is not at fault.
Did you honestly read the article before you first posted? Because it really seems like you didn't, and then said a load of contradictory stuff like "yeah, well, the parents are probably in denial" to justify what you'd said.
I can't understand why the Wii game would call a BMI of 18.2 "fat", other than I guess differences between Japanese and most westerners as Sledge said.
5 seconds of research (there's that dirty word again, guys) tells me that the Wii fit board weighs you, rather than having you input your weight, so it seems likely it just got the weight measurement wrong. After all, the Wiimote isn't exactly a precision instrument.