Just my two pennorth worth as a cyclist, and as a horserider with a very large, easily spooked and unpredictable boy(which does limit where i ride him) It seems obvious to me that the riders attitude is at fault here, and its a shame she could not be traced as people like her continue to give horseriders a bad name. Common courtesy and manners cost absolutely nothing, and sadly my experience has made me realise that the horsey world can be very bitchy and attract some right characters (always female) and before any female riders on here slate me this is just my opinion, formed from my experience.
The horse is not at fault here, there instincts are so much more finely-tuned than ours and as the saying goes "whats in the brain goes straight down the rein"....he was probably picking up on the noutiness of his rider