I would be willing to bet my whole set up that those are not actually made in America. There is no American armor manufacturer (RMA, Hesco, LTC, Highcom, Tencate, hardwire, Point Blank) that sells a 5.3lb level IV plate for that price. Heck Hesco 4800 run roughly $1200/plate and RMA 1192 run $700/plate. Those two plates are around the 5.5lb mark.
Additionally, usually when a company uses "bulletproof" especially on the label, that is a red flag that it is Chinese.
The address on the plate directs you to a surplus store If you look up that surplus store on an
import site, it shows they do get many items from foreign countries. While it doesn't specifically say armor, this proves they have the knowledge and capabilities of buying/shipping goods from China to their facility.