"His primary formal training was in classical piano, which he studied for roughly 10 years from age six, developing a strong sense of music theory, dexterity, and, notably, the ability to play by ear rather than reading sheet music."

The ability to play by ear comes from that 'instinctive understanding of theory' some people have.
You hear the notes and just know where they are in relationship with each other.

Formal training helps with this, but often in weird ways.

When I hear something for the first time, I visualize it in my head as the notes on a piano. The intervals, the key, etc.
That's probably weird for most people, but it's how I first learn something by listening.
My theory is based on my early piano days.

When I play trumpet, I can pretty much just play it, but on guitar, when learning something new on my own, I am transposing a piano to frets between my head and my fingers, which is a difficult task (at first).
But once I play it a few times I no longer think about the piano at all when I play it.
It's just when learning something new.
For bass it's much easier for me because all the strings are a fourth above, but on guitar they just had to throw in that B string!
Yes, I'm weird, and even weirder for sharing that probably. smile

I do not work here, but the benefits are still awesome
Make your sound your own!