I think that's a bit flawed. The purpose of lower education is learn how to learn. By the time you get to university is when you apply those skills to really learn.
Well, maybe the purpose of higher education is to learn how to learn _for yourself_. That is: to find sources, read them, evaluate them, and synthesize them into a conclusion.
I dunno. I passed all the undergrad maths through calc 3, diffeq, linear, and a 400 stats class, ~20 years ago. I could probably solve a calc 2 problem (which was harder for me than calc 3), but I would need a textbook and an hour or two.
Did I learn it? Or did I learn how to teach myself it? I would argue the latter.
I never cared for the "learning how to learn" line. We start from infancy and learn to walk and talk, albeit in that very special way. We are always learning, every day.
For me personally, earning by bachelor's and master's degree was a continuation of K-12 and I made sure to be a top performer. The looming debt was the underlying, motivating factor.
Looking back, I learned most outside after K-12 was done for the day and I was free to explore and get hurt.
That phrase is a thing because K-12 is structured as just learning what the teacher tells you. In undergraduate degrees, the professors are more like guideposts and you can't learn everything in their lectures - you have to figure out and understand the material yourself and most people upon finishing K-12 can't do that.
I also wasn't one of them, so I also had no trouble in college, but I knew a lot of people this applied to.