It is meant to be a catchy phrase to get your attention. You are focusing on the actual semen on the tummy, they are focusing on the type of scene in the movie or the act in the bedroom in an effort to warn a woman that she should not think it is safe.
Women should not say, "Well, I can't get pregnant because the popshot is on my tummy." because there may still be sperm in her vagina even when the popshot is on her tummy. This is what they are trying to say.
It is a common message outside of porn in any family planning clinic, and they use very similar language; which I am sure was seen and copied by somebody at the AIM clinic.
_________________________
--Some of us look for The Way in opium and some in God, some of us in whiskey and some in love. It is all the same Way and it leads nowhither.