I wrote for a music ezine sometimes, and once I interviewed a artist and asked him to say hello to our readers on camera. Since the ezine had no YouTube channel back then, and we were in a hurry, I uploaded the video to my own channel.

YouTube must have thought that, since it was a short (~20sec) video with a person's face depicted prominently, the person had to be me and updated my profile image with a snapshot of this video that actually looked like an intentional profile image. Maybe it was just random, maybe they actually tried to select a fitting image.

Geez, this is a little invasive. Must be an additional "marketing feature" to coerce you to upload a profile picture. Who'd have known a userpic is so highly valued in the social data market.