If you read the original article in Nature you soon find the core of the issue:
"The first is that many if not most standard assessment systems globally do not reward an understanding of reasoning — that is, how a particular result was arrived at (the stories behind the maths and science). They reward a mastery of the method and an ability to get the right answer. Second, relatively few teachers are skilled at teaching reasoning and describing maths through storytelling, and of those, even fewer teach students from low-income families."
Mathematics is a study in patterns, and reasoning. Not in getting the answer to artificial problems, or mastering the huge number of tricks that seem to make up mats "textbooks".
If you aren't teaching understanding, you have failed.
If your students don't ever experience finding a pattern you have failed.
If you think that memorisation has any value in a maths classroom, you have failed.