I have finally figured out exactly where this skewed idea is coming from.
Javen, you are misinterpreting two different terms as meaning the same thing when they do not.
You are reading the popular use of "half" and term "children from international marriages" as meaning the same thing.
"Half" in popular usage does indeed usually refer to mixed Japanese-western individuals... However, the "international marriage" referred to in the statistics is something else entirely. While it includes the parents of the "half" children, it also includes all the other much more numerous non-western international marriages.
The statistics are only talking about the international marriages. The sites talking about "halfs" are referring to children of a very specific subsection of those. Just as not every fruit tree is going to be an apple tree, every international marriage is not going to be western-Japanese... However, every apple is going to come from a fruit tree and every western-Japanese marriage is going to be an "international marriage".
This sort of warping of meanings isn`t really uncommon - but it is entirely incorrect.
In the end, the fact is that only a small number of the international marriages in the "1 in 30" figure are between Japanese and non-Asians. Only those can potentially produce half-western children. All the others will be invisible as Japanese-Asian "halfs".
Really, you should go to Japan and see just how many "half" children or western-Japanese couples you spot. It sure won`t even be anywhere vaguely close to "1 in 30"
, even in the most saturated expat areas in Tokyo.
But you are welcome to keep constructing this dreamlike vision of a Japan where half of every elementary school class is mixed, instead of the reality of maybe 1 in 1000, if you`re lucky.