Whether you believe his reasoning or not, I think it's an entirely valid reason to sell. He needed cash, his entire liquidity is in $TWTR. What else is he going to do if he needs personal cash, take a loan?
You could still run into issues. Imagine twitter stock crashed and you took out a large loan, you're still on the hook for that amount and now you don't have any assets. I would also assume that the ventures that he claims to be going into (charitable donations/VC funding) would require you to have the assets in hand.
If he believed in the stock, why not?