Either the Chinese didn't anticipate the Indian response (possible) or the Chinese screwed up. Oli in Nepal is about to get deposed over being too anti-India. There's Indian propaganda offices complaining that Pakistan is about to get isolated with China, but I'd say that's just Indian political masturbation.I agree with he's using it politically, but whether or not they planned on sending Indian soldiers to die who knows.
After having studied the terrain, I don't actually think India poses such a threat to China via the Quad. When you consider the location of New Delhi, India is potentially another Taiwan or South Korea.
If China is seriously upset at Indian moves to try to contain China, China can simply move a bunch of DF-16s and DF-26s to the Tibetan Plateau. The DF-16s can keep a vast segment of India under threat of ballistic bombardment, and DF-26s can be used to threaten Indian attempts to use the Indian Navy to threaten Chinese shipping, given that DF-26s based in Tibet can cover almost all of India.
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I think my mistake here is that I've traditionally been too pro-India; as I've said elsewhere I am ethnic Chinese with vague connections to India, and I like Indians very much. But because of the terrain issue, India is neither a serious threat nor assailable to China.
The Chinese Foreign Ministry's attitude seems to have it right, this entire thing is a stupid sideshow. I'd venture that China set it up entirely to distract the Indians from Modi's coronavirus incompetence.