Yeah, I don't doubt that a good part of DC's bounce was genuine (worth noting that most of it came from those who had voted for various smaller right-wing parties in 1946, not from "moderate" left-wing voters).
And very clearly non-voters as well.
The strategy of tension, yes. I think much (most? All?) of the mentality of that was home grown, even if it was obviously endorsed by foreign intelligence agencies. I think what the DCs took from the 1948 landslide was that they could keep their ridiculous ramshackle party in power forever if they could maintain a permanent sense of fear amongst the aforementioned basically apolitical practicing Catholics (who could so easily have otherwise turned on them) and so creating an unbreachable vote bank. And eventually the logic of this...