When I was in graduate school taking a class in Reference Sources, the hardest question we had to solve was to prove that a certain "person" did NOT exist. It seems the major "Who's Who" biographic sources often planted faux biographies in order to catch less prestigious Who's Who publications that secretly copied their entries. This false name appeared in many sources, and the search finally came down to not finding the person in the census records where and when he was supposed to have been born. Even that source isn't infallible, of course.
Major reference sources and biographies, in addition to the second tier of "Who's Who (in Electrical Engineering," for example), often duplicate "facts" unknowingly. We can't fact check everything we read or hear, so we depend on "authorities," for whom most of their information is reliable--but not all. That particular sentence about Muggsy Spanier looks like a hangover from an earlier Wikipedia entry on Bix.
But, hey, correcting something that's wrong in the record--that's the fun of it!