Never heard of that before! It sounds as though someone was very, very lucky...
I doubt whether it would have been a take-off or landing incident - some very low flying, perhaps?
Mind you I did hear tell that tyre marks were once found on the VASI boxes at Scampton after a Vulcan had gone around in very poor weather.
Back to 'bang seats', there was once a thing called the 'short rig' or somesuch. We visited Finningley (long before it became a navigator farm) and the Vulcan OCU gave us a demo. One of our number was strapped into the short rig bang seat and the pins removed. The instructor told him to pull the handle, the next thing was a bang from a .22 blank to simulate the canopy firing. Then the sequence continued - it ended with the seat shooting about a foot up the short ramp to which it was attached under the effect of compressed air! The look on the victim's face was one of total shock - I'm sure he thought that he was about to go through the ceiling!
The sheepskin seat covers and more particularly the arm rests made the Vulcan seat far more comfortable on long flights than the JP or Hunter T7 seats of similar design - and infinitely more so thatn that bondage-fetishists delight, the Mk 2 or Mk 3 fitted to the single seat Hunter! Rocket seats were even better, because they didn't need such a firm, non-compressive seat cushion as the earlier 'gunpowder' seats. The Hawk seat was a truly excellent and very comfortable design, compared to earlier seats. But the simple safety lever in the Folland seat fitted to the Gnat was much safer than all those wretched pins in early MB seats!
Fortunately I never had the cause to need a MB (or Folland) let-down!