Looking at how chonky his wrist is, I suspect that “original OP” is quite a big lad and that this isn’t his first schnitzel sandwich. Suspect it’s more “plump thumb” than a double-joint.

I get weird creases when I do the motion of holding a hotdog as well. Something about moving the thumb over making the skin wrinkly.
Although that is a a very defined big wrinkle where I have lots of small ones, so I guess you’re right.