Has that happened more than once? It may have been unrelated. Correlation not equaling causation and all that.
By the way, I always take my couple to the bedroom (or early in the game, to the room with the ratty sofa) before trying, so they don't have to walk so far. Also, before I do that, I get one of them to prepare a meal and I feed everyone. I also make sure both parents are feeling fresh. I'd like to say I don't make them try when they are exhausted, but that would be a lie.
If I have a spare sofa, I block the doorway off with it, which doesn't always work to keep them there and the kids out but sometimes it does. I keep the kids busy elsewhere - in the shower, or watching TV or playing on the computer, or if one persists in entering the parents' room, I just drop them in a far corner of the yard. I haven't noticed that having a kid in the room - or even on the bed - changes the chances of having a baby, but having them in there offends my tender sensibilities.