Why are we thinking of FB as some monolithic entity? Isn't the most likely explanation that some low-wage contractor in the Philippines saw a picture of a naked girl and flagged it? That contractor may not even know the historical significance of the picture.
You're in a low-wage job and have to look at horrifying shit all day, every day. Are you going to let the one image through that maybe will cost you the job that you really need?
Unlikely. A lot of publicity was generated when the original photo was removed. Not only was a photo removed, but the newspaper employee who submitted it, IIRC, had their account suspended. So that's at least two levels of decision making. Then (as linked to in the OP), the newspaper's editor made a public appeal that was well-read in media and tech circles.
And now this, involving the Norwegian prime minister. I don't think the higher levels of Facebook are ignorant to the issue at this point.
You're in a low-wage job and have to look at horrifying shit all day, every day. Are you going to let the one image through that maybe will cost you the job that you really need?