Don't take no chances with people like this. Lock the windows and drive away. If they follow you, call the police and drive into the nearest garage, blasting the horn. What's the betting they were filming the car so they could use forged plates on another, stolen vehicle? Not that? So what other reason would they have to film? It might be lawful and it might be a public place, but their actions appear to suggest their motive is far from innocent.. if they're reading this? Come here and provide an explanation!
If true, then this fills me with disgust. I wish you'd captured the incident on camera - I would advise to always have one at hand. If they sped up hear the horses, may I ask why did they then apparently slow down to allegedly hurl abuse? Or where they hurling abuse as they passed? I am glad it was reported to the police so that it can be kept on file in case of future use. I really would recommend carrying a phone (on silent naturally so that it doesn't startle the horse), as a means of communication as well as potential evidence gathering. Our roads don't need this kind of needless aggression and if this person is being an ass then they deserve to be filmed doing it - and prosecuted.
Don't take no chances with people like this. Lock the windows and drive away. If they follow you, call the police and drive into the nearest garage, blasting the horn. What's the betting they were filming the car so they could use forged plates on another, stolen vehicle? Not that? So what other reason would they have to film? It might be lawful and it might be a public place, but their actions appear to suggest their motive is far from innocent.. if they're reading this? Come here and provide an explanation!