The question i should have asked first is what you plan to focus on in the story: the man himself or he's a part of a bigger picture? (the world and life of some alien planet, the war, colonization of the planet, the life of the people in the space ship etc.) What's the story mainly about? Maybe all these details I wrote about aren't necessary.
So far the guy sounds like a very creative & inventive person, a perfectionist, workaholic and a child at heart (infantile like a teenage boy) and an annoying know-it-all .. does he have friends?
I wonder what toys he could make.. it’s interesting!
And such a person left with no protection on the planet.. it can be real fun for him if he's used to work on his own - no superiors, regime or orders.. He can use his own brains to find out the reason of the mass killing of the squad while waiting to be saved.. if just to kill time
Why is he so bad at using weapons? Is he a gun-shy, traumatized or just averse to it?
Any pets or electronic "pets" he made for fun? Oh, you see, I'm so determined to see the guy as a human. In fact, it may be not important at all..