In another article, they say that the stampede was set off when chunks of concrete fell from a construction project. The horses are enured to the sounds of London streets, but evidently they’re not OK with falling construction debris.
There was broken concrete rubble sent through a chute from an upper story floor and landing in a dump truck. That is a sound/experience unlikely to have been replicated during the horses’ training. I have also read that the white horse was known to be skittish/spooky and had kicked a soldier in the head during the coronation parade. I can’t imagine any of the horses will be returned to service after this adventure, even if physically capable. It’s like having red flags all over your resume.