Hollye, in 2.05 when Killian is posing as a blacksmith, doesn't Mulan say that he joined a few months prior? So he's probably not completely lying about being a blacksmith then right?
Having not seen the episode in a while, I don't remember how long Mulan said he'd been around, but considering Hook only had one hand and was playing up the injury, I don't think he was doing any smithing in the camp. He just told them he was a blacksmith that lost his hand in an ogre attack and needed asylum.
I'm sure if Hook had wanted to learn and become proficient at blacksmithing, he could have, but I kind of doubt he did. However... Do we know what Brennan did for a living before deciding to adopt the rowboat? He could have been a smith, and Killian had knowledge of the occupation from his experience of having a blacksmith as a father in order to help him sell the ruse??