Right. THat means they are left handed players.
Most rockers (both bass and guitar) play
right-handed; meaning they're strumming with their right hands, while chords are fingered with the left hand. This is how guitar/bass is taught, as it uses the dominate hand (this being the right, as most people are right handed) for strumming.
Now, for people like Sir Paul McCartney, he is a
left-handed player, just like Floyd and Janice.
I am one of those weird annomolies as I'm right handed, however I play left handed. I think this might have something to do with my many years as a band member - as a trumpet player, I finger the valves with my right hand; when I played trombone, slide was right hand; the only time I struggled was when I was playing sax cause I had to use both hands, but even when I played piano, I was better at doing chords and melody with my right hand then left.
Trying to play correctly was extremely difficult for me, so I switched to left handed playing and it works.