The author is confusing standard anti-aircraft missiles with nuclear tipped missiles. The SA-2 is an old anti-aircraft radar guided missile, not a ballistic missile. It is unable to climb to a high enough altitude for an EMP detonation, and the warhead is small. It is also relatively short range.
Now, there are ballistic missiles currently made by our enemies in NK and Iran which might do the job but the SA-2 is not one of them. If they could mate a nuclear warhead on such a missile and program a proper detonation point at the right location and altitude, that scenario is quite possible.
The SA-2 has a 300 pound warhead. We had atomic bombs one third the size in the ‘60’s. Something similar launched from the coasts would do a very good job on the US with EMP. It would no t have to hit Omaha. Nevada and Ohio would do just fine.