This was interesting, and speaks to my own experience.
In high school, I did the local quals for the international math, physics and chemistry olympiads. I did quite well on the physics and chemistry ones and went to the international versions as part of the Swedish teams. On the math one, though, I plain sucked. In post-processing, I've realized that what happened was exactly what this article talks about. The math questions were questions where I just went "Huh? I have no idea how to even approach this," because my math education had largely only prepared me for solving specific kinds of problems. I'd never been exposed to things like proving theorems or other kinds of creative thinking.
The first math competition I entered was an interesting experience. There were so many completely foreign concepts like sigma notation that precluded me from even trying to answer the 'tricky part' of the questions. Luckily, the proofs came out on a later competition, after some good math competition coaching by the quizmaster.
In high school, I did the local quals for the international math, physics and chemistry olympiads. I did quite well on the physics and chemistry ones and went to the international versions as part of the Swedish teams. On the math one, though, I plain sucked. In post-processing, I've realized that what happened was exactly what this article talks about. The math questions were questions where I just went "Huh? I have no idea how to even approach this," because my math education had largely only prepared me for solving specific kinds of problems. I'd never been exposed to things like proving theorems or other kinds of creative thinking.