My guess is, in the immortal words of John Lennon, these guys have "blisters on their fingers", although more discreetly than he did.
While the legendary Django Reinhardt, by all accounts, loathed playing the electric guitar during his 1946 performances with The Duke Ellington Orchestra, I've always wondered how those gigs sounded. As it turns out, the recordings from them have circulated, and are available, due to the wonder of YouTube. The answer to that question is. . . "gadzooks - this is indescribably wonderful", as well as signature Django.
Listen and learn.