Was your rear mount flat against the seat tube?
It looks like the sharp edge of the mount block was digging into
the tube and the tube got crushed.
Also the paint is rubbed off so was it loose and sawing on the tube?
Maybe save the frame by putting a tight fitting piece of pipe/ tubing
down the seat post.
An extra seat post all the way down to the bottom bracket might have
saved your frame?
Originally Posted by MysterySandwich
Here are some pics
I'm pretty sure I tightened the rear mount quickly, I should've bought that torque wrench...: