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.
I am not sure why people are expecting market movement whenever he tweets something. I mean, market movement is a combination of different factors and this tweet shows it's only one factor in the overall picture. When the market is already in a volatile state (the tail end of the bull market), and there are other factors contributing (El Salvador accepting BTC, economic tensions in the world) then an additional tweet can seem like it was the one that cause some movement, but it may have just tipped the scale a bit, that's all.