yeah I was wondering that myself! It's all very well saying 'on good authority' and not dishing who that authority is!

I've not found anything about the stones being used by the racecourse myself - I'm willing to believe it, but that doesn't mean they weren't recycled from a prehistoric use? They're pretty fancy stones with their holes and wiggles (and those shapes can be perfectly natural, I wasn't disputing it) and naturally attractive to people wot like stones I'd have thought.