Yes, that is Ben Palmer playing the organ! When I used to know Ben years ago, I knew him as a bass player. But he also plays excellent guitar in almost any style. In our band dotCombo, he never touches a bass. I also play bass, but in dotCombo I only play the organ (with bass lines played on keyboard). Todd Proctor always jokes that “I play in a band with two bass players, but neither of them are on bass!”
Back in the day when musicians were a valued commodity, studio musicians could make a lot of money if they could “double”, or play more than one instrument. Due to synthesizers and drum machines, a lot of doubling became obsolete. When I was in New York, the typical phone call went “Do you play acoustic bass and electric bass?”, then “Can you read music?”, then “Do you have a car?” If you could answer yes to those three questions, you were in the money- it was rare to find a bass player who doubled on electric and upright and could read music.
Some musicians learn a second instrument out of necessity. Drummer/composer Art Lillard composes at the piano, and carries a keyboard in his van so he can cover piano parts in case an unreliable keyboardist doesn’t show up. Tim Smith sings and plays keyboard, sax, flute, and drums in order to be a well-rounded musician who can jump in whenever needed. Other people learn a second instrument for fun: Todd Proctor sits in on organ and bass on monday night jam sessions when he isn’t needed on drums.
Guitarist Brad Maiani doubles on piano and saxophone. He once had a personal studio where he would record complete songs on his own.
For me, learning the organ was just something I always wanted to do. But now I can double on organ and bass- two instruments which are luckily in pretty high demand.