How did bud get the idea that Herman e calloway was his father?

Bud believed Herman E. Calloway was his father because his mother had a flyer for Calloway's band that had "Herman E. Calloway and his dusky devastators of the Depression" printed on it, and Bud's mother had written a message on the back saying "Bud, not like the other Herman E. Calloway, this is your father." This led Bud to believe that Herman E. Calloway was indeed his father.