Reasonable people will. Because reasonable people know how adrenaline spikes work.
You get surprised, and almost immediately adrenaline hits your blood stream. Your eyes dilate and your ability to focus goes way up (paradoxically, at the same time some people experience lightheadedness). Your heart rate and blood pressure shoot up, Oxygen supply to the brain cranks way up. You begin rapid, shallow breathing. Stored glucose is pumped into your blood for quick energy. You may get tunnel vision, focused entirely on the thing that scared or surprised you.
And this lasts a while. Certainly longer than 6 seconds. Then it starts tapering off, but generally doesn't fade away entirely for about 20-30 minutes.
Six seconds is no time at all, in fight-or-flight terms. So of course reasonable people are going to weigh the shock and surprise into a person's reaction in the first six seconds.
p.s. If someone else were in the home with the lad, say a girlfriend or roommate, a protector's instinct may also have kicked in. Think mama bear or Michael Oher in The Blind Side.