Expiration date on crypto makes sense: a crypto algo and more so the implementation is only a timelock, at best, because they become increasingly easy to attack with time.
He could have signed a stock sw dev NDA form that suited everybody.
But what doesn't make sense is that they would sign him on with an NDA that expired, knowing full well that he could then go on and tell people that the FBI had put a backdoor in something they helped to design.
I would wager that they didn't know "full well" that they were going to request a backdoor. Remember this is the US Government we're talking about. That kind of foresight is rare and even when it does exist the left hand doesn't know what the right is doing and expiring NDAs could occur. All it takes is the person making the request to assume, "Hey, he's doing US Gov crypto work so he much have a permanent NDA. I'll go ahead and request a back door without double checking the terms of his NDA."
IF the allegations are true, I am on the side that says he misinterpreted the NDA. There could be reason to believe that the NDA had to do with his working with the FBI but the backdoor was a separate entity.
Either case, its all speculation. Hopefully this isn't a stunt to discredit oBSD. Some serious combing will be done in the code, I trust the oBSD team will do their best to clean up any mess that exists. We will all have a better oBSD after this.
He could have signed a stock sw dev NDA form that suited everybody.