Well it depends, you will find that there are many philosophers that do not believe in free will at all, that we are the sum of our experiences/genes/external environment and the act of decision making is just an illusion, that we never really had a choice in the first place.
On the other side of the spectrum philosophers will argue that the act of logically thinking through any issue, and coming to a conclusion is proof of free will. Both arguments do have merit, they are too extensive to go in to atm.
I believe that the truth lies somewhere in between, you are very right in a way he did not have a choice, but the result of the situation lies in the decision that he made. The boy chooses the act will result in the best possible outcome. I don't think that is the point though you wanted to make, it is that we cannot judge the boy.
I think what you are getting at is that God does not have the right to judge us about certain acts of wrong. But that is why God judges the heart, which is far deeper than the action. And this is why no man is beyond redemption....It is why in many respects God might consider that single kind action from a hardened hearted, burdened man as a greater act of kindness then a Christian dying on behalf of his fellow Christians . That is why good actions alone will never get one into "Heaven", because a person who just acts good is just the product of a particular upbringing/environment/genetics. And this is why the bible says that our righteousness is as filthy rags, because none of us are capable of an entirely selfess act.
I think that you are drawing a comparison between the threatened boy/soldiering with Hell/Christianity. Think of it this way. If I were to hold a gun to your head and say 'believe in God or I will kill you' You are no more likely to believe in God. It would be like trying to run through a brick wall, just down right impossible. I know that feeling because I have been there before. Hell MAY* and I emphasize may, serve as a motive for following God, but it does not explain people's belief in God. Belief in God/heaven/hell must come prior to fear, because you do not fear that which you believe does not exist, agreed? The same principle applies to any other selfish motive, something external must occur to create that initial belief in God, assuming that the person actually believes in God and it is not a case of Pascal's Wager. People might say, no the gun is different. You are right the gun is different, because the subject can physically see the gun, their fear is rational, and yet belief in God still cannot be created, like an off/on switch.
Belief in God/heaven and hell must come before that fear.
At which point we cross into the realm of free will in respects to belief in God. Which is an entirely different subject. I won't go into it, I will just say, and this is a little off topic. Some Christians will tell you that you need to know Jesus to be "forgiven" or to get into "heaven" or what not. Assuming that Jesus is the key, do you think that knowing Jesus is restricted to reading about him on a piece of paper? Absolutely not, it is far deeper then that, which is why I believe God is accessible through other means and mediums.