I am not a fan of the Guardian, but according to the subject of the article (they call him Li), he is a dissident and was under active investigation. I don't think they would have just let him leave
thats fair, but from an outside perspective (from either country) it looks exactly like how the US treats its dissidents. i doubt someone like julian assange would get better treatment.
also, i dont know how they defined "dissident" in this case but its vague enough that i wont judge too hastily.
There is ample evidence that China is suppressing its own people, including prohibiting emigration. One good source among many is the Safeguard Defenders, an NGO focusing on China.
You'll find many good sources, including here on Lemmy. The situation has even been getting worse in recent years.
China is pretty egregious about taking away passports/not letting its own nationals leave its borders. Sometimes because they are political dissidents, sometimes because they are being retaliated against in some way, etc.