The phenomenon is interesting, although the connection to UI is a little vague. Still, I think author has a good point.
Take bevels for instance. They may be considered a visual "noise", and in flat design they are frowned upon, but how do I know where I can click (push a button)?
Similar thing for window shadows, they help to recognize the window boundary.
If it communicates something helpful or necessary it cannot be considered noise.
The idea behind flat design is that we don't need to have a wooden texture to understand that something is a button.
The problem is when you forget to communicate that something is clickable/interactive, which seems to be a major issue with current flat design implementations.
But let's not forget that back in the day it was fashionable to only show that items were interactive through mouse hover. So the problem with designers forgetting useability is hardly something new.
Take bevels for instance. They may be considered a visual "noise", and in flat design they are frowned upon, but how do I know where I can click (push a button)?
Similar thing for window shadows, they help to recognize the window boundary.