The CNN report was quite vague about the information he government wanted. I suspect it would also take the airlines some time to properly add it as part of the process (ie, at check in) to OLCI, kiosks, agent screens, etc.
im also not sure the value of asking if people have been to China in the last 48 hours unless you are sure you are going to get accurate responses. Even of the people who have, who is going to admit that if they realize it could cause them trouble? It’s like when they used to ask the question in the early 2000s about whether you packed your bags yourself and whether it has been out of your site - is anyone going to admit this, particularly anyone who has nefarious intent?