For the First, even Wikipedia warned that it lacks citations and verification, so I don't think it should be considered as a "creditable source". Also it's only a tiny portion of Xinjiang.
For the Second, even if we consider it 100% true, it doesn't really support the original claim from that interview article, in several ways:
1. It's a small portion of Xinjiang, and the claim _implies_ that the whole Xinjiang was "formerly East Turkestan before the Chinese invasion of 1949"
2. The Second ETR was pro-communism, pro-Soviet, pro-CPC, and against the rest of Xinjiang that's under RoC control. In 1949 CPC won the civil war against RoC (KMT), took control of all of Xinjiang. So I don't see in anyway it could be claimed that China invaded ETR in 1949.
One thing I don't understand is why do those condemn China's treatment of Uyghurs have to add the (likely dubious) claim of China invaded Xinjiang in 1949. It's not like doing a domestic (cultural) genocide is something "better" than invasion and genocide, so why add some dubious claim to your legitimate claim?
> One thing I don't understand is why do those condemn China's treatment of Uyghurs have to add the (likely dubious) claim of China invaded Xinjiang in 1949.
The best-organized Uyghur groups outside China are various separatist organizations, so they have a natural advantage at getting journalists together with eyewitnesses while putting their own spin on things.
So it's not like they're adding a dubious claim to their legitimate claim, rather they've been making the same dubious claims all along and it's just now that a legitimate claim has been added that people are finally listening to them.
https://en.wikipedia.org/wiki/Second_East_Turkestan_Republic
Of course, it's Wikipedia, so you'll have to dig through its references.