YIKES JJ
As someone who was once a salaried administrator for MSNBC back when they operated about 200 message boards (there were seven Mods), I can tell ya, you don't just delete or edit posts when someone you know sends an email complaining that what another poster said isn't true.
You are obligated to find out the veracity of what was said before just deleting it in what would seem like a personal favor.
From reading your post, it sounded like you were saying that the only reason you deleted that post is because the object of the post emailed you, and since that person is a personal friend, you deleted the post. Which begs the question, if someone were to post something about any other poster here, whom you don't know, and they emailed you saying it was a lie, would you delete that post too? (See where I'm going?) It's all about APPEARENCES and it would APPEAR that in this case, you don't know or care if what was said is true, but you deleted the post in question only because it insulted/hurt a friend of yours.
People in the public light accept, as part of their fame or infamy as it were, that other folks are sometimes going to say things about them that are unkind, unfair, and even sometimes, untrue.