Guessing from the information in the thread @ActuallyARegular linked to, Musk had been thinking he no longer required a personal assistant for a while. Apparently the assistant in question believed her duties commensurate with the senior execs at his companies and asked for similar pay. I have no idea who was right. I think if he didn’t need an assistant anymore, he should have just asked her to change her position in his organization. Again from the thread, a lot of people thought well of her skills including apparently Musk.
I suspect he saw this not as a mind game but as an objective way to evaluate her for what she was asking. From all the stories I’ve read of him, he sounds like he treats people as engineering problems instead of fuzzy human relationships. It sounds like his mishandling of the situation, which quite understandably probably came across to the loyal assistant as a betrayal, was more his loss than hers. You can see people in the Quora thread who’d met her professionally even using it to ask people to reach out to her to get in touch with them, presumably with prospective offers.
I do agree it was a dick move. But everything I’ve read of Jobs suggests to me that Jobs was a dick despite knowing how to people, and Musk just isn’t any good at peopling. I could of course be wrong. Just my read.