According to Wikipedia, Hinault's biographer William Fotheringham (a writer on cycling and rugby, for The Grauniad among other publications) wrote that the nickname originated from Hinault's early training partners, Maurice Le Guilloux and Georges Talbourdet, who would use the term to tease their younger colleague. Le Guilloux used it once in front of Pierre Chany, a writer for the French sports newspaper L'Équipe, and the name stuck. Hinault himself (says Wikipedia) claimed that the term was originally supposed to mean no more than 'mate' or 'buddy'; but he later embraced the association with the wild animal.
Also according to Wikipedia, the word "blaireau" is also used in French to refer to a shaving brush (which of course is traditionally made from badger hair). I would suggest that there can be little doubt that the nickname, when applied to Bernard Hinault, refers to the animal rather than the grooming aid.
© Haydn Thompson 2021