I'm pretty sure I made it clear how they fight on their DALpedia page. They shoot flaming metal chunks out of their arm, and usually move at a slow pace, but occasionally make quick dashes. Using the term 'flew' for them running wouldn't be suitable, as their movement isn't nearly as graceful as flying. Like, look at their picture.
Plus, I think he killed them way too easily, even though I believe he's supposed to be one of them super-dudes (and I know everyone wants their character to be the strongest next to Retan and be break the bones of mortals by poking them and rip phone books apart with their eye lids) but I don't want the steam demons to be thought of as cannon fodder NPCs and be able to be killed in one attack by everyone.
Retan is an exception as he's more of a plot device than a character, as stated in the rules. Razz