"Why does it seem that every article that refers to UHD say that it is "more than 4 times that of HD resolution". Taking the numbers given in the above article, UHD is 3840 x 2160, or a total of 8,294,400 pixels. Actually, that is EXACTLY four times the resolution of HD's (1920 x 1080) 2,073,600 pixels. No more, no less."
If it's the true and original 4K format (4096x2160) used in digital cinema, that is actually true, however people just follow whatever what other people said and use 4K and UHD interchangeably and at same time become confused, just like this article.
In general, the term 4K shouldn't be used, it's not hard to know 3840 is not yet 4000, it should just stick the term UHD. People didn't call FHD as 2K back then, so why it's now all of sudden use the cinema format and called 4K? Only because when it was introduced there was no erroneous media use the term to tell general public, once it's stuck, it's hard to break.