Haha no, you have not misunderstood at all! I was just driving a point and I did no calculations whatsoever, by that «50" is almost 10x 7"» I did mean that 50 is "almost" 70 and nothing else x) As your calculations show, it's actually a much bigger difference in area, but that stat seemed enough to make my point and easier to understand :)
Thank you for actually thinking about it and taking the time to do the math ^^