In other armies its standart kit, exspecially in the artillery as with these chinese guys. But its not neccerically a "bulletproof", usually the vests of these kinds are just normal anti-snarpell vests. We wore almoust equal vest ourselves and it was mandatory to wear when near the howitsers.
Also what is interesting to see that PLA is apparently starting to adot the western style helmet. The model that the few guys are wearing is superior in artillery operations as it allows you wear earprotection-suite (note the word suite, single earplugs to be stuffed inside your hearing canal don't give you any protection when firing howitsers) and the helmet on at the same time.