Toast.

Warpage doesn't tend to show up easily in photographs, but the cracks and paint flaking off behind the lug points are a definite tell tale sign.

Usually this is from a head on collision. I have seen frames fail on the DT right behind the butted section just from load and use, though it was quite rare. Happened sometimes during the early TIG welding days, when they tried to make the butts too short, at the same time that very thin gauge brittle heat treated tubes were being used for the first time. There was some other reason for a failure there that I recall, but I forget what it was exactly. Something about not matching compliance with the fork. Anyway, I digress. Almost certainly from a collision.

If there's no visible or detectable distortion or cracks, and it's 531, it's probably actually OK to ride. 531 is pretty ductile and tough. Even so I wouldn't buy it myself.