B.B. King’s guitar technique drew from many sources, both direct and indirect.
At first he functioned primarily as a vocalist, making little idiomatic use of the instrument; in subsequent recordings the influence of T-Bone Walker became quite apparent.
He also adapted embellishments used by earlier blues guitarists (Lonnie Johnson) as well as those of jazz guitarists (Charlie Christian, Django Reinhardt, Bill Jennings). King’s distinctive finger tremolo was inspired by Bukka White’s bottleneck style.
This according to “B.B. King: Analysis of the artist’s evolving guitar technique” by Jerry Richardson (American Music Research Center journal VI  pp. 89–107.