Not really sure what this means....
It means (but you're just being your "new cosmos" self here, right?) that dealing with a regular song form and a steady rhythm are among the traditional ways in which one judges a jazz musician's skills. Not the only ways, of course, nor ways that are or ought to be exclusive any more, but traditional, even if they are (or are on their way to being) outmoded. Thus, I would think, not a cause for "not really sure what this means" puzzlement, genuine or "be fooling with you."