Billy Strings made an unexpected return to the stage during Primus’ May 31 show at Meadow Brook Amphitheatre in Rochester Hills, Michigan. The appearance came just weeks after the Grammy-winning guitarist broke his left fibula and tibia in a backstage skateboarding accident. At the concert, Strings joined Les Claypool, Larry “Ler” LaLonde, and drummer John Hoffman for a short guest set. Fan-shot videos showed him using crutches before sitting do…