Tim Urban has a great essay about different levels of prep people do for talks [1] which he wrote when preparing to give a Ted talk. Musk's talks are on the "Wing it" side of prep while a Ted talk is suppose to be on the "Follow an exact script - Happy-Birthday-Level memorized" level.
[1] https://waitbutwhy.com/2016/03/doing-a-ted-talk-the-full-sto...