No this is not common. At least not super common I think. Idk. I've never seen such content and I'm Chinese. And I've been on Xiaohongshu for years (since 2018).
I've always been "small" because I'm petite, thin and I was a former dancer. So keeping fit and maintaining a good weight was crucial (as a dancer).
I saw someone tried to argue that dancers in China are "physically fit" and being skin and bones are what dancers look like.
No, they don't!
Even at my skinniest I was never skin and bones. At my skinniest, because I was depressed (after being hospitalized for falling and breaking my leg), I was 42kg at 153cm which was slightly underweight. But my family and friends got me help and I was back to my usual 48kg about a year later. Honestly, even at my skinniest at 42kg, I don't look like skin and bones (the girl in the pic in the comments must have weighed less than 40kg I think).
Plus, none of the girls and boys in my dance school were ever that skinny until they look like skin and bones. Our dance teacher would bench us (and get help for us) immediately if we looked like skin and bones.
Most of my other Chinese female friends are all small and thin too. But not THAT thin.