What Tesla did with bitcoin could be considered market manipulation, and that's a serious crime considered by the US government. The fact that the company invested $1.5B and make it public that bring a lot of investors to bitcoin, and after that, we see how bitcoin has a crazy jump in the prize, and now they sold the 10% when bitcoin was on its ATH.
As a reference, I will leave this link:
https://www.fbi.gov/scams-and-safety/common-scams-and-crimes/market-manipulation-pump-and-dump-fraudSo, the question is, did tesla make market manipulation and you think the company will be charged for it?
In my opinion, I think Tesla as an individual or a company has the right to do what others are also doing(buying and selling of bitcoin) as long as the law within his country permits.
One thing is obvious here, Tesla is a big name(my thought) thus his actions in the market is capable of causing some kind of excitement, that's why the price of bitcoin went up after $1.5b investment.