The subtitle is for the narrator's words, and he wasn't saying the fuselage shown belongs to a J-20. Even if he did say that, he'd be wrong or lying. That's clearly a J-10. The general contours, none serrated panel lines, and the airbrake match J-10 perfectly.
It's perfectly normal and customary to point out when an image has been shared before. In general, the community prefers new and/or never before seen images that are informationally revealing or are aesthetically pleasing. Sharing an old image is ok and even encouraged if it reveals new information, or when it's relevant in the context of a particular new development, or if it assists in making a point or demonstrating a fact during a discussion, among other scenarios.
unofficial data, F-16A F100, Climb to 50,000 ft in a min, so 254m/s, whereas F-16C Blk 50 with F110-129 can do approximately 320-335m/s clean. We don't know which variation of J-10 he flies, config and engine, so that's that.