Elon Musk won't sell his bitcoins, he tweeted this and we see no big movement in the market. There was a time when his tweets had big effects on the market. This guy is losing his value by promoting Dogecoin.
Yeah, he won't sell his Bitcoin or his shitcoins, who cares. I think that in this forum we don't really care what he says, although it must be recognized that he has a short-term influence on the markets.
With his sheer influence on social media, lots of people are actually clinging to his advice. Remember the time when he tweeted in favor of DOGE coins? The price of the latter skyrocketed to the point that lots of people profited from that time. From my experience alone, a friend of mine had like $100 worth of DOGE and after the tweet of Elon, he profited like $800+ on a single day, in which he immediately cashed it out.
Though we do not actually care about his choices, we cannot ignore the fact that he has great short-term influence (like you mentioned) on the market that could potentially dictate the price of these cryptocurrencies.