Fecal bacteria poop give you a vaginal infection. Whether for penises, toys or fingers the rule is that nothing that's been sex the anus can go back into the vagina.
Pooped during anal - GirlsAskGuys
There's no need to feel gross or embarrassed about it. If you engage in anal sex, this sort of thing is to be expected. It doesn't mean you had a bowel movement, there was just probably a little bit of left inside.
Some women give themselves an enema beforehand to stop it from happening. Some guys use a condom.
Pooped during anal...
Kudos to your guy, he handled it exactly as he should have. Any mature guy knows and accepts that girls poop too and it's nothing to get freaked out about. If a guy anal handle a little poop he shouldn't engage in anal during the first place.