You're not an idiot..
He just got excited that's all. Snorting is typical of a horse that is unsure of something and his adrenaline is pumping.
Painthorsemares describes it beautifully :)
Don't lose this horse's focus though, young lady. An unfocused horse that goes chasing after quads does not sound all too safe and mindful of his limbs. Could get himself, or you, hurt.