It was, but something tells me that the m/m in and of itself had nothing to do with the low rating, because:
On that site there is a specific section for slash/yaoi (it's an anime fandom), and if someone didn't want to read slash, they would skip over it into the het section.
And also, the rest of my fics there are also slash (but not the same pairing as the other fic), and they all have a five-star rating and good reviews. Even one (different pairing) that has even rougher BDSM scenarios.