There is a difference in the results for "portraits of European" and "portraits of Europeans".
"portraits of Europeans" contains a large number of non-European faces.
"portraits of Europeans" contains a large number of non-European faces.
Which are the same that are showing up via the articles about art of european history from the original result. Again, this is just keywording working against your expectations. The relevant results for these keywords lead to articles discussing the presence of non-whites in European artwork.
What you envision for the results of the search terms are apparently different than how other people envision them. In this case, the search is considering portrait paintings, not portrait photos or anything, and from there, it looks like the most popular results are these articles.
Search for "[pictures, photos] of european people" or just "european people" and you get more pictures of white europeans. Unsuprisingly, once you search "paintings of european people" you start to get the aforementioned paintings once more.
This isn't a conspiracy or social manipulation, it's just that there is apparently enough discussion and interest in older european paintings including black people that searches related to paintings of europeans returns a few results with black people or indian people.
http://medievalpoc.tumblr.com/post/62747229987/marten-van-my...
http://afroeurope.blogspot.ru/2010/08/history-of-black-peopl...
http://realhistoryww.com/world_history/ancient/Misc/Art/Addi...
Yes, blogs and tumblr sites but these are valid results.
What do you make of the results for the search term "American inventors" which returns largely black inventors.
Though, admittedly after Edison, Carver, Whitney, Franklin, Moorse, I ran out of people I consider "famous" inventors, so the list doesn't really impact me. I do question their inclusions for some inventors though...as quite a few were not born in the US, and only came to the US later on, but that's my own hang up)
I also suggest that this is a prepared result and not a search result so I don't hold it to the same scrutiny. I treat it the same as an advertisement.