Nerdy McNerdface
Hmph
Apparently, "Hagane" is the central character of an obscenely overpriced video game on SNES of the same name. Considering the lack of references to anything else, it's likely they the two are related in some way. It might have something to do with Riley being known for Steel-types and Hagane being a robotic ninja. The pairing was named prior to April 5 2007 as this post shows, though I can't find where, when or by whom it was named. It should also be noted that it is likely only the Japanese names of the characters were known when it was named. While certainly not a perfect composite by any means, it's not impossible to see a similarity between "Hyouta x Gen" and "Hagane."
I can see how both reasons make sense - the latter more than the former. I think it's a mix of both - the two names being merged in such a way because they both sounded similar to Hagane when together, and Hagane happened to be made of metal. Thanks!