////To say that bluegrass doesn't come from English sources is wrong. To say that it only comes from English sources is wrong.///

Bluegrass is not descended from Celtic music. It bears no resemblance. It is descended from minstrel music. Many of Bill Munroe's sidemen were former minstrel men and so were the proto-bluegrassers like Uncle Dave Macon. Bluegrass is based on the African-American banjo tradition with some old-time mountain thrown in as well as ragtime, blues and jazz. But at its root is African-American banjo music filtered through blackface minstrelsy.