Yeah, crypto is not as regulated as "classic" markets. But powerful people do it anyway. It's not just as obvious most of the time. After a big dip he announced helping Doge dev team (which is new, project was dead for a long time), so it's going up again... oh well...
After the dip after he says doge was just a husle, he also post a pol on Twitter whether tesla should accept doge as car purchase payment.
Basically it seems he deliberately increase and decrease the price of coins