You may have skimmed over this bit in the article then:

"the international A-size system now starts with A0 paper, with sides in the correct 2‾√ ratio, but with exactly 1m2 of area, or as near as you can get with whole millimetre side lengths (1189mm 841mm, to be precise). Then folding or cutting it a few times until it is conveniently desk/folder sized gets you to A4, hence the ‘4’ bit in the name."