He's not making a decision this way. He had already decided to sell and is just being attention seeking as usual
I'm far from being a finance expert, but I think it makes sense that he wants to get around the catch-22 that practically every one of the richest people face:
They are worth billions of dollars, but mainly because of stocks they own. But if they want to liquidate, the stock price will drop considerably, so their actual value is much lower.
So Musk is seeking to sell with an 'explanation,' which he hopes will mitigate the price drop of his stocks when he begins to dump them.
Agree?
ETA: YES, I see that one of the nation's biggest finance expert DOES agree with me, and I just missed his memo:
Just a way to sell stock without tanking the value. Brilliant really.