What you're looking at here is not an 8K resolution screenshot of Mass Effect 3. It's one-sixteenth of an 8K resolution Mass Effect 3 screenshot.
Go ahead and expand that top image. It's a full 1920 x 1080, or what we've been calling full HD for several years now. 8K resolution is 7680 x 4320 — 16 times the number of pixels.
Here's the full picture, capped by Redditor DarkLiberator. For the full effect, right click the image, choose open in a new window or tab, and then expand it to full size.
See the choice ring at the bottom of the screen? It's ok, I didn't either at first.
According to DarkLiberator, the game's framerate was pretty much unplayable at this resolution, so don't expect me to start building an 8K gaming machine any time soon. Thankfully he's compiled a 64 image gallery on Flickr (you'll want to download the full-size images) so I don't have to worry about it.
Mass Effect 3 8K [Flickr - DarkLiberator]