I mean random as in the two colours are selected at random.
I think it's not really relevant to select colours in a void. Colours are good for a purpose. This is especially relevant on websites. I love yellow but I would hate it when it's used for text on a white background. Stuff like that.
I certainly agree that context is important when picking a color. I don't think the conclusion is that whatever color is selected the most should be used for everything because it's the most popular. But when presented with two colors the way the site does, there is generally one I prefer over the other. Whether this preference information is actually useful is a whole other question.
Ultimately, wouldn't that just see which is the most popular background color? Pixel-for-pixel the background takes up the largest percentage of screen space on most websites.
Though I would also be interested to see what the most popular background colors are. My money's on white and off-white.
You could, instead of counting pixel-by-pixel, count once per specified color. Eg count #000000 once per css rule it's specified in, once per image it's used in, etc.
That would have made a lot more sense than what they're doing. I'd really like to see the outcome of that. Not this random comparison.