the translation "man of steel" is often misunderstood. Stalin does not translate to "that made out of steel", but rather "that belonging to steel".
however when you look at the amount of power that man had, you might think it's not that absurd to call him that. On one hand the man had the power to kill off any one, relocate them, or change virtually anything in the country. On the other hand somehow through his reign of terror he had made a country that was a backwoods agrarian swamp with no military or industrial power to speak of (I mean come on, how the hell do you lose a war that you alliance wins in 1 year?!), and turned it into something that could take on the Nazi war machine for 3 years (other than the African campaign, that was where the Germans fought), and could be the first to launch man into space.
on topic of Steel's man being a dictator, actually there is a clear statistic they don't much tell you about in school, that in most "half-developed" countries (i.e. ones with high degrees of traditional corruption, like say Argentina), a dictatorship always achieves more (at least in the first decade) than a democracy does. (that does not mean you should surrender your freedom to vote- just that democracy isn't always a cure, just like everything else in life.)