Seeing as I was attacked a couple of weeks ago, I can explain what's up with that guy:

It's happening fast. Very fast. You have to be trained AND you have to be on your guard ALL the time to react in time
It's literal down to instincts (trained or innate) in these kind of situations
And even trained people will be slow to react if something happens that they don't actively expect to happen
You can daydream all you want of being a hero, in real life it's your body that decides (freeze or run away(i ran away)) what to do
your mind catches up minutes (MINUTES!) later