I don't think Frankie said Pete couldn't play guitar, but he is not the best guitar player by anyone's admission! Yea, he does a mean Petey Mill, but not the most accomplished guitarist out there!
For some interesting info, Keith Richards actually plays with only 5 strings on his guitar, and it is tuned like a 5 string banjo, a harkening back to his first insturments! That's why most people who try to emulate his style of playing find it so hard d to follow!
Yes, I'm a professional musician, and am typing this from a gig right now! I play a little guitar, and most other insturments as well, so im a fair judge of guitar playing!!