True, should've said 'because the NSA was involved in the design of the standard'. They never classified it (the design), but I think they did in DES.
And it makes sense, especially at the time, to harden against differential cryptanalysis because it's the more efficient method, scales better and requires way less computing power than trying to bruteforce the key. But pushing for the shorter key suggests they were trying to leave themselves a reasonable chance of succes if they had to go last resort and try to bruteforce the key, as they were one of the few actors at the time that had access to enough computing power.
And it makes sense, especially at the time, to harden against differential cryptanalysis because it's the more efficient method, scales better and requires way less computing power than trying to bruteforce the key. But pushing for the shorter key suggests they were trying to leave themselves a reasonable chance of succes if they had to go last resort and try to bruteforce the key, as they were one of the few actors at the time that had access to enough computing power.