Orthogonal mean perpendicular or at 90 degrees from each other. In chemistry it refers to orientations in space. For those of you that learned atomic theory, there are three different "p" orbitals shaped like a figure 8. The orbitals can be thought to run along a coordinate axis (with the nucleus at the origin), one along x, one along y, one along z axis. The orbitals are orthogonal to each other. The functional ramifications are that if two orbitals that are orthogonal from two different atoms overlap, they will not form a bond since the overlap integrals essentially cancel out. Another way to think about it is that two orthogonal vectors will never intersect - they head in different directions.
So with all that jargon out of the way, my application to the artistic comment is that I see two "vectors" described. In the first case, a rigid set of rules are applied for right and wrong tone and the player plays accordingly. In the second case, an artist has a vision that they are trying to realize, and they play accordingly. Those two approaches to me are fundamentally orthogonal, and the latter is about art while the former is not.
That isn't to say that art doesn't have or need rules. But as my wife tells her students (she is a sculptor on faculty at CalArts), you have to learn the rules so you can break them. Many students show up wanting to "do their own thing" and not learn history or classical approaches. That doesn't really work in the long run. On the other hand you have artists who learn the rules and then are held prisoner by them. Many of these are great technicians and can be pehnomenal players, but likely are not artists. It is a dynamic process though, so the two could meet even if they are orthogonal. Probably the whole curved space thing
as always, ymmv.