If Tesla actually did not sell its BTC holdings, then today's plunge could have seriously affected its quarterly earnings (I'm not 100% sure how the accounting works, but they may have had to revalue their BTC holdings which would show as a loss on their P&L).
Tesla's addition to the S&P500 has gone a long way to propping up that share price and while one quarter in the red wouldn't be enough to boot them from the index, they're still in a precarious position when it comes to profitability. I don't think Musk is stupid enough to risk the share price on a Bitcoin bet.
So this is a roundabout way of saying "Musk probably has a considerable vested interest in keeping the price of BTC above $40k".
But I also believe - without proof, mind you - that they have sold at least 50% of their holdings at a profit anyway, so their downside is capped.