@Grischa
You're 100% right!
Chess, Rubik's cube and other puzzle games, have nothing to do with either elegance or inelegance.
@sinkingship
It's not just that he solves a 4 by 4 Rubik's cube, he solves logical puzzles/games in various fields, and multiple ones that require previous knowledge/practice.
Which indicates that he's knowledgeable in various fields, just as it was said earlier, he learns a lot and every day, which you call smart.
But all that aside, I think what implies how smart he is, is how they emphasize the fact that he solves these problems, that are generally looked upon as intellectual activities, with ease.
And while yes, in and on itself the Rubik's cube does not imply that someone's smart, in my experience the general opinion does align with it's usage as an indication for intelligence/smartness.
So imo the place of the Rubik's cube is appropriate.