The speech and singing regions of the brain are separate from each other, which is why this works. It also can work for people who lose the ability to speak from brain damage.

It’s wild how adaptable the brain is. Some dude was out there just living life when he had a head mri after a car crash (iirc) and found that he only had a brain stem.

To quote ancient words of wisdom: “Everybody’s sayin’ that the Scatman stutters but doesn’t ever stutter when he sings. But what you don’t know, I’m gonna tell you right now that the stutter and the scat is the same thing, yo, I’m the Scatman.”