Is there any way to know for sure when something is a digital artifact?
Yeah, find the original source video, play around with color controls, brighten and contrast, you’ll end up seeing blobs—those blob areas were less uniform when the CCD camera picked them up, pixels get tossed in lossy compression, that’s how video compression works—by removing mostly redundant information.
Now, take that original video, recreate the process of crop and zoom, then reencode (probably with web quality params.) You should be able to tell things got a lot more uniform and/or distorted. Again, loss of information during compression.
It’s like a photocopy of a photocopy. Each iteration, progressively worse.