I will accept, for the sake of the discussion, the statement that we know little about what Bixs personality/character. I will make two points.
First, let me make the general statement that Bix is not unique in the fact that we know little about the essence of his character, that he is an enigma. Is there a musician from the 1920s who died young and is not an enigma? Consider, for example, Eddie Lang, another musician from the 1920s who met an untimely death at an early age. He was the quiet half of the Venuti-Lang partnership. We have an excellent discography (which also serves, at least in part, as chronology) Feeling My Way by Ray Mitchell. We have some biographical information about him, including a comprehensive medical report about the circumstances surrounding his death. We do not know his political preferences, what books, if any, he read, we do not have interviews of him (or do we?). We know that he enjoyed gambling and billiards and that he was a good husband. But what do we really know about him? Is Eddie Lang an enigma? I dont think so. And why not I ask? Perhaps because there is no aura of fascination surrounding him, and historians/fans have not attempted to uncork all facets of Eddie Langs personality as they have tried in the case of Bix.
Second, let us not forget that Bix was a musical genius. By definition, a genius is unknowable to the common, average individual. Superlative individuals, as McPartland tells, are not like us. Their creativity, their obsession with their field of endeavor, their dedication, places them apart from the average individual. Richard Hadlock (Jazz Masters of the Twenties) articulates these concepts very effectively. He [Bix] was, like many intelligent men who are preoccupied with their lifes work, absentminded and sometimes removed from all that went around him. Even among jazz musicians, a notoriously individualistic lot, Bix was regarded as an odd duck. Read what Wingy Manone tells us about Bix (Trumpet on the Wing), He was always talking about music, telling us, Lets play this chord, or Lets figure out some three-way harmony for the trumpets after the job tonight. It seemed to us [note he is talking about musicians in general, not just himself] he didnt want us to enjoy our life. Certainly, Bix was not like most musicians, he was a genius, totally dedicated to his music, and I dont find it surprising that normal musicians viewed him as different from them.