I'm 99% sure anyone who uses internet is being spied on. Facebook, Twitter, YouTube, WhatsApp, emails, and text messages all run through a scanner that checks for "suspicious" words and phrases. I'm sure if you sent an email that contained a maximum clearance military password, you would get a phone call in a few minutes. Then you would have guys in suits with guns show up at your house.
User data is collected and stored by phone, media, and internet companies forever, AFAIK. Even if they claim to delete it. This data is usually used to give you ads and websites based on your personality. It can also be used against you if you apply for certain jobs, or other things. Nothing online is hidden. Everything sent online is easily availble to government entities, such as the CIA. All your passwords, bank account information, everything you ever said online or on the phone, it is all stored. There are warehouses full of giant computers that stockpile decades of information of everyone.
The thing is, people don't bother searching through all that data, unless they have a reason to do so. Then they pull your info and they know all about you.
So, China already knows all about these athletes. Their political views, everything they ever said about China. They just run a word search for "China" through their data. And I'm sure they have hidden cameras in public places as well. With facial recognition. Same as USA or any developed country. Hidden cameras are all over the place.
It's not that every camera has some guy watching it 24/7. It's like a guard in a prison with 500 cameras. He is not watching any of them. He is watching YouTube and playing games on his phone. But if there is an incident in cell 126, he goes through the camera footage for cell 126, reports it to his boss, and goes back to his YouTube and games.
And drones with telescopic cameras are all over too. Even infrared cameras. I met a woman in the IDF. Her job was spying on Arabs with a drone. She could see what the people were doing inside their homes. USA and China do the same. Most any country actually. The drones are over 40,000 ft. Above civilian airspace.