The individual decides. Yet, who is to say the concept itself can not be the deciding 'factor.' Why can't "art be art unto itself"? True art comes to one, it is not always "discovered" and labeled as such.
Human pride has such a strong influence towards, "what is art" it's sad to realize. Determining when something worthy of being 'art' "should be" ignored or building a "perspective of art" for sel-centered reasons.
Categorizing 'art' is limitation, all too human.