Its not burn in, and they have to try really hard to see it
Read the thread pointed to in the article. The reports are of a non-uniform black (changing from black to grey in a relatively smooth transition, top to bottom or bottom to top), for which you need to turn the brightness right down and view it in a darkened room for the effect to be visible.
Nothing like the Google problems, which can be seen in normal light and is obviously where the menu bar was displayed. Perfect? No, but not in the same ballpark.
Colour transition off axis was something they pointed out even before release (proudly, they claim to have reduced it below normal for OLED), so its not like that should have been a surprise for anyone either.