That's official Chinese state ideology today. However, whether an autonomous but tribute-paying region is part of a country is in the eye of the beholder (see f.e. the fiefdoms not directly under Ottoman control in Europe, or Korea for long periods of China's history). What's more, Tibet was not the only region getting free during the Chinese imerium's 20th century weakness: there's Taiwan (overtly threatened by One China ideology) and Mongolia (covertly threatened), too.

It is not under occupation, though I do understand some ethnic Tibetans (like some ethnic Basques in Spain, ethnic Corsicans in France, ethnic Tamils in Sri Lanka or ethnic Pathans in Pakistan) think it is

The only reason I haven't told you are channelling official Chinese state ideology is that I think you are channelling French national state ideology.

More to the point, China's settlement policies (which didn't 'finish off the job' so far only because a lot of settlers can't stand the climate and move back East after a few years) and the behaviour of the settlers cannot be called other than occupation. To not rely on Western media, I tell what a friend told who travelled from Beijing to Bombay as backback tourist. For example, every village is 'doubled': the original village of the native ethnics is sided with a Han Chinese quarter, and power is held by the latter. The problem is not just the regime, it's Han Chinese nationalism, as evidenced by tourists: the most disrestpectful in Buddhist temples weren't from Texas but from Shanghai & environs.

_{*Lunatic*, n.
One whose delusions are out of fashion.}