There are certain older fannish circles where "gen" used to mean "everything that is not slash or NC-17 het". However, I'm surprised to find that in a recent fandom like SPN.

There are also some people who feel that "gen" does (or should) encompass stories which are primarily gen but have minor references to sexual relationships. But in this case, it sounds as if the relationships were the point of the fic, so ... I have no clue.