My Boyfriend just called me "Mom" during the middle of sex.

Yeah, i don't know what to make of this. My boyfriend and i have a pretty healthy sex life. We do it at least 2-3 times a week and this is the first time something like this has happened. But anyway, we were having sex, he was close to climaxing, i could tell because he sped up and started moving faster and squeezed me tighter.

And right before he did, no mistaking it, he started grunting "Mom." I know for sure that's what he said. He said it at least 2 more times. "Mom. Mommy.".

Afterwards, he rolled over and went to sleep, but i couldn't get that out of my mind. I asked him what the hell that "Mommy" stuff was, but he denied it. He said he didn't say anything at all. I told him i know what i heard but he just ignored me.

What on earth was that? Any possible explanation?