I think that the licence of the times can be invoked in this case. Mao was nothing if not an exceptional self-publicist, and many westerners in the sixties and seventies saw him as a man of the people, [SNIP], but it's a lid that would have been pretty tightly shut when The Mind Of Evil was written for TV.
That's an interesting point, as The Mind of Evil's writer, Don Houghton, was married to Pik-Sen Lim (who plays the Chinese captain Chin-Lee in the story), so you'd imagine he'd have slightly more knowledge of the situation in China, via his in-laws, than the average UK writer (or armchair marxist, like fellow Pertwee writer Mac Hulke). ISTR that she was from a Hong Kong Chinese family, but don't quote me on that...
As for the UNIT dating.. I'm not going there... mainly because I'm also a late-dating person, and have got a sore throat from shouting at friends who favour the early-dating theories!