manzico,
It's pointless and futile to attempt to compare images viewed at zoom levels other than 100%. That's because the only accurate and true representation of your image is when viewed at 1:1, i.e. 100%, which shows the true pixels in it.
At any other percentage zoom, either pixels are discarded or they have to be made up, invented.
In the case of your two screen shots, however, they happen to be absolutely identical.
I confirmed my visual observation by downloading your images, placing one over the other as layers and setting the blending mode to DIFFERENCE. The result was a pure pitch-black image, meaning the differece is ZERO.
I even added a threshhold adjustment to maximize any pixel differences, setting the threshhold even at an extreme level of 8 (yikes!), and there's just no difference between the two whatsoever.
Thus, at this point I have no clue as to what you are seeing.
Since screenshots are really not taken from the monitor's screen at all but from the digital signal sent to it and before any monitor profile correction is applied, I can only surmise that your monitor profile is bad.
Remember that Photoshop is a color-managed application, while Apple's Preview.app is not. Photoshop uses your monitor profile to convert the image before showing it to you; non-color-managed applications like Preview.app do not do that.
I won't comment beyond that because of two personal, subjective opinions of mine get in the way: (1) I don't think much of iMac screens, and (2) I detest Lightroom and have no desire to go into a discussion of how it shows you the images on screen. 