I would say no—rather, their hands are executing two parts of the same task: playing piano.

That's like saying a wind player is multitasking when they blow air while simultaneously moving their fingers.

If you mean a different piece in each hand simultaneously, then yes, I'd consider it multitasking. Until the pianist practiced doing that enough to think of it as a single piece in their head, that is.

The accompaniment hand is practiced to the point where it's automated, so not truly.