Barry Ancelet has heard more Cajun musicians than he can remember. A retired professor of French and folklore at the University of Louisiana at Lafayette, Ancelet hosted “Rendez-Vous des Cajuns,” a bayou-style, Grand Ole Opry broadcast, for more than two decades.

But when Jourdan Thibodeaux came over his car radio last year, Ancelet had to park and call the DJ. Weeks later, Ancelet...