This could happen because previously people explicitly tagged you in their photos, so in new photos you're auto tagged
On one side it is weird, on the other side it makes sense. For example: Einstein is not an FB user. But if people upload photos and tag him it makes sense after a couple photos FB learns what is Einstein
FB is doing with facial recognition what Google is doing with image recognition for captchas.
Calling that "weird" is an understatement, considering what's going on there; Users are asked to identify friends and family for facial recognition, to train an algorithm that FB then monetizes for all kinds of advertisement and surveillance shittery.
The whole thing is imho way past "weird" and firmly in dystopian territory.
On one side it is weird, on the other side it makes sense. For example: Einstein is not an FB user. But if people upload photos and tag him it makes sense after a couple photos FB learns what is Einstein