very rare for horses to fully attack something that can prey upon them, like humans, dogs etc.
usually limited to self defense, feeling cornered, ill mannered stallions- especially near mares in heat, and true wild ones feeling trapped.
that horse in vid was an alpha horse keeping intruder out of the herd, physically behaving as horses do to each other. that man could not read horses body language at all. not his horses, no business going in there :-]
still unusual. but the horse could've been made to back off with almost anything in hand, like a stick or length of rope to swing.