I wish your story and Oubergia's could be required reading for all who act as if the small size of the equine lessens the potential danger.
Since we live in an area with a multitude of deer (and deer hunters), and drive regularly on a woodland trail, this is something we need to keep in mind. So far Mingus has dealt with anything scary or confusing by stopping, which I think is a very sensible reaction. He's seen a lot of deer on our property, but who knows how he would react when driving? Perhaps he'll think they're llamas, which he's fine with, but which total wig out our neighbor's QH.