The deterministically derived ECC constants are derived by seeding a hash function with an extremely high entropy input (> 100 bits), and taking the first usable result. This is effectively the same as choosing the parameter. The NSA had freedom to specify this very high entropy seed value, and could have done so by iteratively trying seed values until they got a curve that weak using techniques only known to the NSA; it's just a way to disguise the origin of the curve by making it sound random. The situation with Kobolitz curves is only slightly better.