> "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.