well it's not. You could shoot an arrow at a different person each time. And you get to decide your target after seeing the effects of your previous shot. So if you kill the guy on your first then you know that before picking the target of your second arrow.
This is true of all full attacks, flurry of blows or not. You can choose to attack any valid target with any of the attacks. You could punch an adjacent character, fire a bow at a different character, then punch the adjacent character again (if you have three attacks).