Did Concorde really fly above 55k feet as mentioned in this report?
Yes. The extra height was necessary in order to reach lower pressure air, and thereby reduce drag, and heating of the airframe from supersonic compression of the air.

Concorde's windows were extra small, so that if a window did blow out, the air compression system could actively compensate by pumping air in faster than it could escape, until the pilot completed his emergency descent.

More details can be heard on this podcast.