what @elonmusk is doing is known to all shareholders if they want to do something, moreover the value is certainly not small and in the stock market they compete with each other between Tesla and Bitcoin. But what @elonmusk is doing has a very clear impact on bitcoin and there has been a pretty sharp increase, but in business we don't know what it does and why it should buy bitcoin.
but as long as it is very profitable in business, of course it will be done even though in the stock market they compete with each other. sometimes it is difficult to read the minds of big businessmen who are very confusing. for them the most important thing is to generate profit for the company.
I think it is not "his" bitcoin but he owns a good chunk of it as well. Remember he is a "shareholder" in tesla as well, probably the biggest one I imagine and he does have a huge chunk of word to say about what the company should do, if he says that company should buy bitcoins, there is really very few that could say no, and if he wants to sell it, there are only a few that can say no as well.
Basically eh runs the company like he is the king and very few can stop him. Plus if company is 100% and he owns (no idea how much he owns) 10% of it, that means if company invests 1.5 billion dollars, 150 million dollars is his shares of the company. That is why I think it is not "his" bitcoins, but if bitcoin goes up, he is going to earn a lot from that too, whatever tesla does that makes profit for tesla would mean profit for Elon Musk as well.
