And by interesting I mean creepy and probably inevitable.
In a third photo, you fly a kite with both parents, but only your mother is tagged. Given the strength of your “tagging” relationship with your parents, when you search for photos of your father the algorithm can return the untagged photo because of the very high likelihood he’s pictured.
So the gist is that it's inferring that a photo with your mother, a child, and another adult probably includes your father. My read of the article is that their algorithm is not doing image recognition of the father, but rather, it's inferring that a photo of your mother and two others probably includes your father due to the close relationships established between you and your mother and you and your father in other photos.
And somebody made that damn robot fish too I had an idea for that back in the mid 90s :( /rant
It'd be neat to reduce the entropy of possible photos by using EXIF data (location, etc.)