I think the article kind of tramples on its own point by showing a very long history of the changes to the Finder’s icon over the years, but I think what it’s trying to say is that it has been mostly unchanged for many years so it shouldn’t change now. It now has a gray box all the way around instead of two blue faces that go all the way to the edge. However, it simultaneously showed that it has been redesigned several times to match the aesthetic of the OS and while this is a larger change than most is still within the same design space.
The actual problem as explained in the first two paragraphs of TFA and shown in the first picture, is that the light and dark blue sides of the Finder icon have swapped sides. For the first time in its existence of many decades, the dark side is now on the right instead of the left. This is the problem.
