Notice in the photo of the cover of the magazine how everything in the background of the model is completely out of focus? In a normal photograph, everything beyond the focal plane will be in focus. However in Portrait mode, the MODEL is what the photographer wants the viewer to pay attention to, not the background, so the point is to de-emphasize the background. A normal lens system will be able to resolve everything beyond a specific distance. . . But not things closer than what you are focusing on.
So, background blur is introduced due to some sophisticated digital image processing. Thanks for the info, I wouldn’t have noticed otherwise.