The 2nd "army" is the terror exporter...the revolutionary guard which protects and promotes the Islamist regime running the country...which is different than a national Army. It would be like the GOP or Trump having an army separate from the US Army. It is not a national army in the traditional sense. It is this organization, not the national Iranian Army which was declared a terror organization.
Now, during an actual invasion of Iran, the goals of the 2 armies may overlap. But absent that, GS is just a terror exporter, is he not? Seems like all he does is travel around the ME helping terror organizations, and when inside Iran, he is merely an instrument of oppression within Iran.
Anyway, just heard a distinction made along these lines on the radio while out for lunch. Seemed like an interesting distinction.