Earlier quoted context omitted.
That would be admitting you are wrong. You can never admit you are wrong, it makes you look weak. If you look weak, you will not get anywhere. This is really how some people think.
If you admit you are wrong in paper/email, isn't it entirely possible that you can then be quoted on it later in an accusation of negligence? In this specific instance for example, wouldn't admitting you are wrong in an email to Arrington immediately give him a solid case to defend himself with in the event he chose not to take it down?
Quite possibly… but which course of action is the most likely to succeed in getting the post quietly pulled?
"Hey Michael, sorry about this, but some wires got crossed on our end. My bad. Apparently…"
or
"Hey Michael, you screwed up. You better pull that post or else."
?