This is the frame with the attached derailur!
I was actually thinking about that as you mentioned that somone may have had work done on it.
It doesn't feel out of the realm of possibilities that somone with the know how to attach a derailur with an ugly bead would do some blobing of brass on a popped seststay cap.
As to the sanding I was actually concerned that the paint stripper would cause problems for the powder coating process. I had read that its toug to get off but I imagine that refers to people who perform a full strip not just spot strips such as this.
Thanks for the link to the thread, I'll check that out for sure!