This is an excellent question. Of course, the point of view of this challenging short story is third person limited, which helps create the detached tone that you refer to. From the very start of the story, it is clear that the tone that is created stresses the normal, factual elements of "fasting" as a form of art:

During these last decades the interest in professional fasting has markedly diminished. It used to pay very well to stage such great performances under one's own management, but today that is quite impossible. We live in a different world now.

The story presents fasting as a now outmoded and anachronistic form of art that is no longer popular. However, to be taken in by this factual tone would be to ignore the very real element of humour that lurks behind this detached point of view. Of course, the hunger artist is presented as a figure of pity, but at the same time we cannot ignore the presence of the absurd. The notion that fasting is an "art" which is presented as an art form before admiring spectators is ludicrous. Likewise as we follow the struggle of the hunger artist to pursue his art to its highest and most purest form, we cannot escape the feeling that the hunger artist is a bit too self-important and places too much emphasis on his art. Kafka seems to be asking deep questions about the nature of art and the fervency with which we lead ourselves into states of artistic excess.