Musk does not like short sellers since at least 6 years ago. When TSLA was having production problems and he was sleeping in the factory. And the short sellers were circling for his blood.
Many big short sellers are not content to just take a short position. But they also release negative press about a company to push the price lower. Sometimes it is warranted, sometimes it is lies.
So short selling is fine in principle, but sometimes the short sellers resort to dirty tricks. Now Bill Gates may not be doing this, but Musk just doesn't like short sellers in general because of it.
Long buyers will try and pump stocks with positive spin news, but when short sellers do the opposite it can push a struggling company further towards failure.
Back then Musk didn't just take those short attacks sitting down, he resorted to his own counter dirty tricks against the shorts, eg. by saying he was considering taking the company private at $420 funding secured.
that's some fine revisionism you got there.