I followed the link and looked at the photos. I could see how it would make that mistake.
1. The Color balance was off: What we call black people are actually just a richer brown. the color balance gave their color more of a real Black/Gray color, the natural color of a Gorilla.
2. The Angle of the shot. The tilted Angle makes it appeared that they are not upright but slouching in.
3. They were making unnatural facial features for humans. They were making funny faces at the camera.
4. The dark hue of the gentleman who was behind shirt, combined with the ladies hair style, makes it seem the body with much broader shoulder.
I expect the combination of a lot of factors created the wrong choice. But computer decision making, while getting good, isn't perfect, but it is often better then not having it because then it wouldn't be possible to catalog the millions of images. We need to accept that computers make mistakes and there should be a way to fix them when they are found.
Many of our derogatory comments come from the fact that we find similarities with something else, so it come to reason that a computer may make an actual mistake that will reinforce such derogatory meaning.