I think your friend is just being kind.

Most people know that there is a big difference between experience in something pretty easy vs mastery of something very difficult.

A rocket scientist acknowledges a concrete guy knows way more than he does about concrete, but also knows that doesn't make him a genius because it's easy enough to learn just being around it. Plus, the rocket scientist also knows that since he knows so little about concrete, he wouldn't even be able to judge if the guy is really a concrete genius or just saying things a real pro would label wrong.

Your example isn't that crazy, but still, you should realize your friend is just being nice.