Okay, this entire guide is silly, and I have no idea where you got your numbers from.
How far away people like to sit away from the TV is entirely subjective. I have a 65 inch 4k TV and I sit 4 feet away from it. According to your guide that's way too close, but to me it's perfect. Why? Because the bigger the screen is to your face, the more immersive it feels. If I'm watching TV and most of my vision is filled with TV screen and I can see everything on screen, to me that's perfect.
I also use a 41 inch TV as a computer monitor, which I sit 2 1/2 feet away from. I always laugh to myself when people say they have a "big" 27 inch monitor. I don't understand why people like tiny monitors, especially when TVs these days are so cheap. Web browsing, video streaming, and PC gaming is so much more enjoyable on a bigger screen.