The app is also "Twitter", the <title> tag is etc. Everyone is going to keep calling them tweets. It's just the logo and redirecting the x.com domain really. Which makes sense IMO (regardless of whether it was a good idea which I'm skeptical), I don't think they should go hard with the rebranding immediately. You need to slow roll it so people don't get confused. The logo is a good start making people notice and get curious without making a big disruption in Google results and mobile app discovery.