You don't need a statistics degree to understand why this faulty article's 88% figure is utter bollocks. You don't even really have to understand how "userbases" work.
Consider the basic case: The only way for PS4 to meet this imaginary metric is if the demographics of the PS4 and the XB1 we're completely identical. If the demographics we're identical, then the size of the userbases would be roughly equal AND distributed equally world wide. Both of which are not the case.
ERGO: The PS4 and XB1 would have around the exact same number of sales, 37 Million = 20 Million
Consider the distribution case: PS4 trumps XB1 in Japan, ROW, and Europe, XB1 is slightly higher in Latin America, and the two are basically equal everywhere else. Unless every country felt the exact same about Ubisoft games, it would again be skewed by regional diferences.
If this faulty article really want to get somewhere, it would use 1 region only. Comparing the two on such unequal terms on a biased metric is obviously going to give it a biased (unreliable) result.