I am also a computer engineer and I have also studied these topics
Have a look at the algorithms then. It is not possible for artifact to produce such big artifacts. What they can do (and in fact you can see them in the images above) is to introduce noise around the edges or small blocks near areas of the image with many different colors due to the quantization step that tries to reduce to much the number of colors to compress the image more.
Artifact should be consistent on the same image. Look at the image. There are lot of artifacts because it has probably been zoomed and compressed quite badly. How can it be that a perfect rectangle appears exactly where it is needed (how convenient) and it has no artifact around its borders?
I don't understand if you are kidding and just like to start useless and meaningless discussion, or if you are serious.
Provide me with an image of your choose and settings for the JPEG compression (or other standards if you prefer) that produce similar results as the ones in the article, and I will believe that you may be right.
It is true that I have not looked at the actual compression algorithms, but it is also true that it is typical for proprietary algorithms to be used by software that is not in the public domain, so I have no way of knowing if the algorithms that I look at are the same as might be used by someone else.
I have no intention to start meaningless discussion - I have simply been involved in some forensic examination of images previously where artefacts were shown to have been created which did not conform in any way to expectations of the investigators - yet they were there.
I am not saying you are wrong, I am just saying that for my own preference, if I were examining this, in the interests of being thorough and not jumping to conclusions (since jumping to conclusions is the single most common cause of human dysfunction that I am aware of) - I would be looking for the original image before personally saying that I was sure either way. I have no problem with you being sure without such investigation - we all have our own parameters for the levels of investigation we will accept of such things before we will consider something to be proven.