I can only surmise that a bus must have mounted the pavement (by a good 6" or so's worth) and slammed into the end of the shelter.
This morning I left my bike in the Park Street Car Park and ventured from there to work on bus like I do occasionally. For the first time today the first bus at the Bridge Street Southbound stop was a Red Newmarket-Road P&R bus; and I was amazed at the route through town that it took me (I stayed on until the Grafton Centre, where I caught one of my usual Green Cowley-Road P&R buses).
(Stops indicated by P-shaped blobs)
The particularly distressing bit about this route is that it takes 15 minutes to get from Four Lamps Roundabout to East Road Roundabout. This map only shows the Eastbound (Newmarket Road) service, as the Westbound route is different.
By comparison, the slightly convoluted route that the Green buses takes seems sane (they follow basically the same route both ways; so I have shown both).
And, just for completeness, this is what yesterday's bus did, which was surprisingly ept in practice: