Increased body armor penetration has been a consideration since at least 2017(page 10), however it was less the driving force back then compared to pushing for longer range, which given that Afghanistan was ongoing makes sense. Increased range and increased armor penetration were both justifications from the start, but it has been interesting to watch which of them was the publicly pushed focus and when. As heated combat in Afghanistan became less pressing, there was more of a spotlight on armor penetration.

But did they say Chinese body armor

No, I haven't found an official DOD document specifically calling out Chinese body armor. Publicly the DOD is going to mostly avoid naming names of a nation it isn't at war with. "Emerging threats" "Peer adversary" "Global situation". But about the time the US was getting serious about the NGSW they were also gung ho about the M10 Booker, a vehicle that really only makes sense for the US to create if it is planning on island hopping combat, and the US was getting super serious back into jungle training for conventional troops. Meanwhile China was showing off it's capabilities. So, yeah. Chyna.

I'm not sure if it's in the program docs but it does seem like a reasonable conclusion. Maybe we'll get some field testing data on its effectiveness in the next few years. Might be harder to find a Russian with real plates by then though, lots of cheap knock-off body armor out there.