When you first start the game, Hugin says "Most items must be crafted. However, due to your recent departure from Midgard, you will have to recall the true shape of objects. Just pick things up and it will all come back to you, I'm sure."

So this means our viking already knows how to build all this stuff, he just needs a little reminder by picking the materials up. So he was a master craftsman, a shipwright, and apparently an honest-to-Odin wizard. With impeccable Viking fashion sense, of course!