To add some context -- when a lawsuit is filed the defendant typically has only 20 days to file an Answer. In that 20 days, he must find a lawyer and get the lawyer up to speed, and the lawyer must draft and file the Answer. The 20 days tends to go pretty fast.
The Answer must include a response to all of the plaintiff's allegations and also any affirmative defenses. If an affirmative defense is not raised in the answer, it is generally considered to be waived (gone -- can't be used later). As a result of the time pressure and a lack of familiarity with a new case, many lawyers throw every affirmative defense they can think of into the Answer (to avoid losing it), and then sort the whole thing out later as time and resources permit.
It seems that is what happened here. The lawyers threw in an ill-advised affirmative defense, and are now withdrawing it after further reflection. It is unlikely that the F/O paid any close attention to the affirmative defenses in the Answer (as they tend to be heavy in legalese), and if he had questioned it, the lawyer no doubt told him not to worry about it, that they would be reviewing them again later.
The continuing question in my mind is why the pax are suing the F/O. Unless he's sitting on a fortune (unlikley), they won't get any money out of him, and considering how badly injured he apparently was, it just seems like piling-on.