This is slash in the sense that yes, there is m/m that is not canon, but it's less about the relationship than it is about the character. It's not a romance, in other words, but there is mention of m/m and m/f in the story.

I think there are many variant definitions, but that is mine. For example, the HP story is Lust Over Pendle is genslash.

I'll post this in your LJ because it looks like that is where you want to discuss this.