The Reagan era was so bizarre that even late-model le Carré can't do it justice. Claire Sterling's work (referenced in the article) was basically hackwork hearsay that came in via two key sources: a right-wing journalist closely linked to the Moonies, and a Tory speechwriter-turned-novelist who believes that he is in contact with Native American shamans via his dreams.
These are not, I should stress, the strangest people who held influence over the intelligence community in those days.
The official CIA judgement on the matter was more qualified, pointing out that the USSR supported "national insurgencies and some separatist-irredentist groups," but did not directly support terror groups (although they did support states like Libya that, in turn, supported and directed terror operations): "[T]he terrorist activities of these groups are not coordinated by the Soviets. The Soviets have on occasion privately characterized certain nihilistic terrorism as 'criminal,' and have urged other revolutionary groups to cease and desist from terrorist acts the Soviets considered 'self-defeating.'"
One certainly could point out that US support for groups like the Afghan mujahideen and the Pakistani government, the Central American Contras and their narco-trafficking allies, and right-wing "Gladio" networks in Europe would have, from the banks of the Moskva, looked a lot like US support for terrorism as well.
But CIA's considered analysis was basically ignored by senior political leadership, including CIA director Bill Casey, and a pervasive and almost hysterical suspicion of the Soviet leadership overshadowed US foreign policy for most of the 1980s, resulting in lost diplomatic opportunities and a few close calls with general war.