I guess there's two problems here. One, if you're not hired due to refusal to sign an NDA, it would be like trying to prove discrimination - very difficult without other cases to back you up, and how many people are refusing to sign NDAs? Probably not enough, in similar enough circumstances, to build a case. And then, you would only be arguing against the exact clauses of the NDA, as it's a fairly well established legal principle that companies can ask employees to sign such contracts to protect their own interests (like it or not).
On the second problem i.e. how do you fight a suit claiming that you have broken an NDA that you signed, it's probably easier to build a case. I reckon you would have to prove that you were justified in doing so e.g. that the NDA was unfairly restricting your ability to perform your job, whether the NDA was with your present or a previous employer.
In this case, it's fairly clear that the person had no professional need to disclose the information. Regardless of your opinion of Apple's desire for secrecy, there's no defense to be made here. It's more a case of arguing to what degree the individual is liable - I would have thought this is more a matter of immediate dismissal rather than taking the guy to court.