Interesting topic. In my uneducated opinion, which amounts to nothing but recreational speculation, art is on a value scale that decreases in proportion to the distance each simulacrum rests from its origin.
Art is only original. A framed painting hung on a wall has less value than it did in progress, sketched in, paint still wet. And, less value still is the material, or even the form, than is the physic process, the interior dynamics, the whole of the first seven days of creation, all within the artist as the image gained materiality from (a qualified) nothing, almost a Self-less nothing into presence.
Now, listening to Bach are we experiencing art, even so far removed from its conception? The answer can be yes when the music provokes movements of creativity, sparks replacing provokes would afford a better analogy, sparks lighting across the night of personality in ways previously unimaginable, literally unimaginable.
When a new participant is drawn by the work to a place original, then there is art. It is proportionate in quality to the ability of the listener to approach, say, Bach as the music formed in his, Bach’s, body. That’s true because no two origins are comparable, each is a new beginning against a (and again, qualified) nothing, not quite an oblivion, but an absense, a state potential with something always on the verge.
A highly publicized art, as in the requisite public relations, can ride on a neutral vehicle if the originating artist is serious about origins rather than transportation. If the artist is serious only about transporting the art to the market place, then the origin occurs in the mechanisms of transportation, while the substance, the painting or score, etc. looses original significance.
So, if the musician in question was sincere in the context of his music itself during the performance in the metro station, then he would have been playing musical art. But it was probably a mix… he was probably equally sincere in the social experiment, which itself became the art. The passersby were the unwitting participants in a work of art that required their distraction, and the performer’s work became ironic, rather than… whatever in the world is the opposite of irony? Sincerity?
It the music hall everybody agreed. The issue of irony may have been present, but so subaltern that only a probing cultural critic could construct (rather than find) it (the construction a work of art in itself). It was a situation where all the audience members as well as the performer were given the maximum opportunity to experience the stupendous first seven days of creation, be artists, each according to just measure.