LOL I don't think it's two separate frames welded together, I think it's just bent and possibly welded again. It looks to me like the upper set of tubes should be welded to the side of the seat post, but they're broken off.

A while back, I started a Just Riding Along community for fun things like this (I know we're not so busy here that it really has to be split out, but I figured there were plenty of people who wouldn't be interested). Which reminds me, I have another contribution from Facebook, if I can find it.

Also we have a frame in the shop right now where the owner claims that it broke overnight. He said he washed it one evening and it was fine, then the next day, he went to ride it, heard creaking, and he discovered that the chain stay was cracked in two places. I'll get a picture Tuesday.