Jim Cantrell says it is true in https://www.quora.com/Is-it-true-that-Elon-Musk-was-spat-on-...

Here's a link that seems to cover the basics of this history (but doesn't seem to get right down to the nitty gritty spitting incident).[1]

[1]https://www.inverse.com/article/34976-spacex-ceo-elon-musk-t...

Ashlee Vance's biography, 'Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future'