He was very negative on Tesla at first, then observed their improvements first hand and realized they were rapidly improving and were willing to throw old things out no matter the investment.
It was only at that point 1-2 years after he started making Tesla content that he bought shares.
He is not delusional enough to think that he himself moves the stock price. If he thought Tesla was falling behind or stopped improving he would simply sell the stock (at lots of profit) and tell people that Tesla is going in the wrong direction.
For this reason, I think anyone who legitimately cares should be quite skeptical of any opinions he has about Tesla and EVs at large.