Remember that he was recovered originally from a table in Zola's lab. They implied pretty well that he was experimented on. I suspect he got dosed with Zola's best knockoff effort to duplicate the Super Soldier Serum and get it working properly. After being "triggered" by the trauma of a long fall, he now has something vaguely resembling SSS attributes. Probably not as good as the real thing, but combined with a cybernetic arm. . .