I don't see that as fundamentally different than any other large Forex transaction. A bit unusual for a manufacturing company, but hardly unprecedented, and for all we know this is just a signal that Musk is betting he can call the Bitcoin bubble, rather than an actual hedge against USD.
I think that's Musk realizing that the announcement that Tesla bought Bitcoin will boost Bitcoin's value. And therefore cashing out that reality by making the trade.
It's not technically illegal afaik, but it certainly is making a trade because of realities inherent in the trading, rather than the underlying.