I'll assume the article is correct for Netflix because their calculations assume the applicable codec and compression schemes of Netflix. YouTube would use their codecs and compression.
I don't know what a "4x Ultra HD" video would be. However, UHD-4K is 3840 × 2160 pixels and UHD-8K is 7680 × 4320 pixels. By comparing 8K to 4K, although the horizontal and vertical pixels double, the total megapixels quadruple.
4K: 3840 × 2160 = 8,294,400 pixels
8K: 7680 × 4320= 33,177,600 pixels
33,177,600 / 8,294,400 = 4
UHD with a factor of 4 would definitely account for a spike in data. Be careful!
Some devices...perhaps Roku...allow you to set the maximum allowable resolution for streaming, such as 720p or 1080p only. That way, you'd get no surprises. If not an option on your device, perhaps in a streaming account.