In China, it's very common for websites to ask people to trust their self-issued certificates. If you want to buy train tickets in China, you end up with this page (https://kyfw.12306.cn/otn) which asks you to trust its own cert.
iCloud is not the only victim here. Google's IPv6 access has been suffering the same attack since September. (IPv4 access has been blocked entirely for 5 months)
It's not a shocking news, however. Apple has already moved [1] some of its storage servers to Beijing. The attack could just be the authorities making sure that Chinese users' iCloud data is actually stored in China.
I'm from China and I just don't know how to refute your last line. Google has been blocked for about half a month now, but average people would not feel a thing about it.
In China, it's very common for websites to ask people to trust their self-issued certificates. If you want to buy train tickets in China, you end up with this page (https://kyfw.12306.cn/otn) which asks you to trust its own cert.