That's a PC on a floating shelf with some shelf brackets for additional support, i have something similar for my case(also have a similar setup for a 43 inch screen in one of the bedrooms), but at desk level beside the desk(no space and the monitor shelf runs the width of the desk). A decent floating shelf, with some heavy duty wall plugs(basic cheap ones just won't hold as well) and screws can do the job, but as in the picture linked in the OP, some support brackets wouldn't go amiss in providing extra peace of mind that it will hold. My shelf can hold my weight(seriously, i used the biggest plugs and screws that would fit) but i added a leg(brackets would work to) below it all the same so i can be sure it'll hold over time(it's not permenantly fixed and i remove it when hoovering).
A good weight test for a shelf is a pile of bricks, as many as is needed to be close the weight of the PC. I loaded my shelf for a few days with the heaviest items i had to hand(4 bricks and a bunch of tools) and it didn't budge an inch.
