Thanks for the new sources, the bilibili video at 4:05 indeed looks like camera in the chaser plane. Now I am back on the original point.You think too much. There is no point to have this much uncertainty if you plan to export it. The AVIC promotion video is on qq video. Although the subsequent missile firing looks out of place, that could be CG. Most of the close up of J-20 are CG.
Here is a second source, at 4:05
Yes, the missile launching looks 99.9% CG to me. The plume tells everything.