From the article itself:
With a 1920x1080 display the iPhone 6 would have taken the crown
This hurts their credibility. Not their ability to analyze and review a screen, but their ability to review an overall product.
The physical size of the iPhone 6 screen has an accompanying optimal resolution for USABILITY. The higher the resolution, the relative tinier you'll see the same icons and font sizes. Sure, they'll be crisper, but you'd have to hold the phone closer to achieve equal legibility, at which point, the crispness is normalized back to being the same as the lower resolution. Plus, the higher res would make touch boxes harder to hit accurately no matter how close you hold the phone to your face.
The only way to increase resolution without making things smaller and harder to read and touch is by also increasing physical screen size OR by increasing the resolution so much that you can use a different pixels-per-point multiplier (i.e. original iPhone was 1, retinas are 2, some samsungs and the new 6+ are 3).
So 1920x1080 would not have made the iPhone 6 screen better in any way except as a tech sheet comparison and for users watching 1080p movies with the screen held really close to their faces. In normal usage, it'd be a worse experience because UI elements would be too tiny (or too big, depending on if they went with 2 vs 3 ppp). The iPhone 6 screen would have needed to be about 2000x1124 with 3 pixels-per-point on a 4.7" screen (or 1920x1080 on a 4.5" screen and 3 ppp) to achieve the same usability and sharper elements.
Note: Pretty sure my math is correct, but the concept stands nonetheless. Screen resolution and physical screen size have an important relationship when considering usability. You can't just arbitrarily make res higher. You have to consider screen size and pixels per point because you want your "9 pt font" and "64x64 touch regions" to look and behave consistently.