I'd rather give Youtube benefit of doubt here, given that Youtube can't profit in China and that Google has had a long history of standing up against China. A more plausible reason for this mishap is that, as I guess, Youtube's removal system is automated and considers user complaints. The propaganda machine of Chinese government, or even China's little pinks, may have figured out a way to game the system by filing lots of complaints.

Was that confirmed to be true? I saw it pop up on Facebook, but it just said “What Google might look like in the future if we allow this to pass” (or something like that)

Yeah, unfortunately. The image I uploaded wasn't from myself, but I confirmed it first hand before posting so it made no difference which image I posted.

There’s really no excusing this, or blaming it on some obscure bug. “Yellow” in HK is very specific these days, and definitely political.