The difference is that Charles Mingus could both play piano and compose, he chose to focus on the bass. Many artists played piano as a second instrument, including Gerry Mulligan, Bob Brookmeyer, Stephane Grappelli, Phil Woods and Dizzy Gillespie, for starters. Mulligan played piano exclusively when he appeared on Marian McPartland's Piano Jazz, while Grappelli, Woods and Gillespie doubled on it when they were guests on the show.
Phil Woods appeared on Piano Jazz twice, though he only played piano on some selections on his second visit, which was a special fundraising edition.