This is what Jeff told me.
Defensio is the name of the program that catches spam and puts it in the mod queue. It also puts the first several posts of new members in there to let us make sure they are ok before they post freely in the main forum.
You just go to the Moderation Queue in the admin panel and click on "validate" then "Submit" to let the program know that it's ok.
You can also right click on the username and select "Trust this user" to make sure that no more of their posts get caught.
Why it marked your's as spam I do not know.