just because horses are much larger than us does not mean they don't feel pain if they are hit.
they are just skin, muscle and bone just like any other mammal - they are not invincible with a rhino hide.
if a 5 year old head butted me - it would hurt!
not as much as if an adult did it but it would hurt all the same.
to say the horse was not bothered is a bit daft - how do you know?
they cannot frown, cannot raise their hoof to rub it better - just becasue it didn't behave as an injured human would does not mean it wasn't bothered.
obviously there was no real physical damage like cuts and broken bones - but have you ever seen a horse with a bruise? no? well you wouldn't ,would you, under all that hair.
i would have loved the horse to turn round and kick him - or head butt him back
as has been said it show what these people see their horses as - sports equipment - and this one 'malfunctioned'