Gao Yang couldn't be bothered to argue with Justin because he was facing a very real problem: he was out of bullets.
A sniper rifle is definitely not the first choice against aerial targets, so Gao Yang didn't carry sniper rifle ammo on him. He was reloading bullets and adjusting his gun when the helicopters arrived. He had four full magazines for the HK417, and as for the AWM, he only had one five-round magazine, which was loaded after a test shot out of habit.
Therefore, Justin made a correct choice to take the AWM, but followed it with a wrong choice by almost emptying the magazine, leaving just one bullet for Gao Yang. This wasn't really Justin's fault because Gao Yang was the one who instructed him to fire.
Looking at the truck at the bottom of the slope, Gao Yang turned and ran downhill, shouting at Justin, "Follow me! We need to get some bullets!"
