Something similar happened to a friend of mine while he was riding. Afterwards the wheel looked like this:


Full story here.

This was not a matter of brake wear.

Rims more commonly fail on account of brake wear. That has happened to me twice, where my rear rim wore to a point where it started to crack and bulge. Both times I felt a whumpwhumpwhump when I hit the brakes and on inspection found a section starting to give way. Nothing catastrophic.