I'm not sure if it's their stance or their first time using a gun but that's a lot of recoil being shown.
I'm going to take a guess. I think it's mostly because they are new and very inexperienced. Even the SMG is seen pushing them noticeably. Take note that it seems they are firing mostly in burst, the first time we saw that shooting mode since the very first CCTV video.
Also, it's interesting that the QBB-95 was seen in the footage. It's the same as previous videos where we saw troops with qbz-191 and qbb-95 as their squad machine gun. It really seems to solidify my hypothesis that they are planning for now to use their qbb-95 remaining stocks, as it probably fullfills satisfactorily the same requirements for the role as the new machine guns.
On a separate note. I think the reason that China doesn't outfit optics on the india border, besides the other reasons others previously mentioned why it's not being so quickly widespread in general, has to do that the Chinese probably are expecting that if SHTF, they will bring in the heavy stuff, like tanks and artillery. They are not so focused on infantry and small arms as USA is. If im not mistaken, we have seen previously footage of the PLA fielding the QBU-191 on the Indian border. That rifle probably would be better suited for long distance mountain shooting that an QBZ-191 with an Chinese ACOG.