I wouldn’t have expected Musk to have read it.

Who said he actually did? The term “grok” is listed in The Jargon File / The New Hacker’s Dictionary. Musk probably read it long ago. …Like every proper geek. Nowadays, every time he drops an epic meme (as kids say these days), it’s a hazily remembered reference to something nerdy from ages gone by, and it just demonstrates he has absolutely no idea about the context.