Critical thinking is something people develop over the years and it starts early IMO. It's not just a 4 year course. It's a whole approach to the world around you. There are many critical thinkers in my experience outside of collage. And I don't see it a problem as such.
Also it doesn't matter how good a critical thinker you are we all have blind spots and biases that makes it impossible to be critical thinkers in all contexts. Will need to look at the study to see how it's actually measuring the critical thinking skills.
Many of those who do learn critical thinking first when they get to college end up getting such a aha moment that they think critical thinking is the same as constructive thinking and should be applied to everything.
You often meet them in the big companies or management. Many of them like to play the devils advocate poking holes in everything around them but aren't able to come up with solutions themselves.
In my view critical thinking is best learned by reading philosophy and seeing how philosophers historically either improved or created new theories. Because here critical thinking and constructive thinking goes hand in hand. If you read the right progression of philosophers through time you end up understanding how they didn't just critique but put forward their theories which could then be critiqued.
In my view critical thinking without constructive thinking is as big a problem as no critical thinking.