No, Notch wasn't alone, even at the very beginning of Mojang: he founded the studio with Jakob Porsér and soon after Carl Manneh. It had 25 employees in 2012, and close to a hundred in 2014 by the time it got acquired.
No venture is ever done alone. Not just because founders are, as the article say, unable to even handle their own emails, but because every single founder in the world lacks talent. We all do. You're not good enough, and you never will be, especially not to hit a billion. That's a fact. Every single human creating has been a collaborative one, and Sam Altman's delusions don't change that.