Haha, I doubt it. It sounds more like a dominance thing to me.
My little guy, Milo has lived with my roommate's male, neutered dog Kody for months now with only Kody doing the humping and even that stopped after a month. Well Milo has become progressively more dominant as the months have gone on. Kody was lying down today and Milo (who is considerably shorter than Kody) climbed up on his back and started attempting to hump him. Kody didn't even notice anything at first, Milo looked a little confused, and it was all over in a matter of seconds, but I found it greatly amusing nonetheless.
Anyway, the point of my story is, it was probably just a dominance thing.