you mean resolution not as high?
explain what you mean by pixel density
"Retina" is about pixel density and distance from the screen. 1080P on a 5" phone display is very high pixel density and probably falls into the 'retina' category.
1080p on a 32" TV across the room is also probably 'retina' because it is a lower pixel density but it is viewed from further away.
1080p on a 27" iMac two feet away on your desk would be pretty low density, even though it's the same 'resolution' as the above two scenarios.
Here are the pixel densities of a few devices:
Current 27" iMac: 108ppi (pixels per inch)
Original iPhone: 163ppi
iPhone retina: 326ppi
iPad retina: 264ppi
Macbook Pro retina: 220ppi
You can see as you get to screens which you use farther from your face, the density required to seem 'retina' drops.
The display you linked to, although it has a high resolution of 3840x2160, only has a pixel density of about 163ppi because those pixels are stretched across a 32" display.
That's the same pixel density of the original iPhone display, and still pretty far away from the density of the retina Macbook Pros.
4K resolution (3840x2160) would provide about 210ppi if it were squeezed into the 21.5" iMac, so that might be a possibility in a year or two. The 27" model would need something closer to 5000x2800 to reach the same pixel density.