.... from Bix's mother to Bix. We don't really know how Bix's mother referred to her younger son. We have letters from Bix to his mother and to his mother and father. Most letters from Lake Forest Academy are signed LBB. There is one from May 31, 1922 to his mother where Bix signs the letter "Leon." There is the unfinished letter of Jul 30, 1931 where, according to Evans and Evans, the notation "Bixie's letter, never finished" was added in his mother's handwriting. Are there samples of Bix's mother handwiring for comparison? There are also a couple of letters from 1931 to his parents signed "Bix." In a 1930 letter from Bix's father to Marie Louise, Bix is referred to as "Bickie."
The bottom line, we don't have documentation that speaks to the question of how Bix's mother referred to Bix. Perhaps, it was Bickie or Bixie, or Bix, or even Leon. It is possible that in talking to the reporter, she was trying to be more formal, hence the name "Leon." She also used the name "Bix" in the first sentence of the quotation. We don't really know.