In which country, and where did they graduate from? Not all colleges are alike.

Critical thinking is not something that can be taught. It's a family of skills that can be learned through years of practice. Academic degrees usually place a heavy emphasis on practicing the subset of critical thinking skills relevant to the field. And you can often see the differences in the graduates. People who studied CS, mathematics, law, and history tend to approach problems in different ways.

Of course, not every graduate meets the standards of the degree they got. Many don't have sufficient internal motivation to work hard and learn. And universities often lack strong sources of external motivation. No matter whether it's the government or the student who pays for the education, there is a heavy pressure to have people graduate in time, even when they have not reached the expected standards.

I would be interested in looking at such a course, all the ones I saw were pretty dull.

I found the most systematic way of teaching critical thinking is to do a lot of maths.

That might have been sampling bias. If they were hired and not fired quickly, they had probably already passed some test for critical thinking. This is like testing whether familial wealth affects SAT scores by comparing the results of rich and poor kids at MIT.