The word Grok comes from the novel Stranger in a Strange Land where the main character is Valentine.

More likely is that they took a bunch of good usernames to sell - if you pay for their most expensive subscription one of the features is that you can rent a better username now.

It's extremely unlikely Musk was personally involved in any way in the decision on the username.

In a normal business? Sure. When it comes to Musk and Twitter? Less sure.

Add grok to that list, it's pretty much his pet project