I've heard of other CIA stuff like this where they think doing some "superstition thing" will spook people more. But it's often just the CIA being hamfisted and ignorant about it. They're white supremacists so of course they think "ooh lets get 'em with fake vampire stuff". The article actually says:

Reports revealed that the townspeople who were once either indifferent or sympathetic to the Huk cause were undoubtedly terrified.

Yeah, that tends to happen when you murder a bunch of people and dump their bodies in the village...

the “eye of God,” which would be painted on a wall facing the house of suspected Huk sympathizers in the dead of night. “The mysterious presence of these malevolent eyes the next morning had a sharply sobering effect,”

Another thing that doesn't require "superstition" to be scared of, the CIA eventually did this type of marking for death elsewhere (i.e. Vietnam later) and it was probably clear what was going on.

The CIA operation played into the narrative of “Godless Communism” or perhaps it was just proof of enduring Filipino culture and folklore. Whatever the operation proved, it did show that even amid rebellions, wars, and political plots, Filipinos—past and present—are still scared shitless by aswang.

Not once did they even mention that literally murdering people and placing their bodies in villages is scary no matter what, and that this stuff was clearly evil. This is just typical CIA 'isolate guerillas and terrorize and murder their "sympathizers"' type stuff. The Wikipedia article for Landsdale says he was directly told to do the same thing in Vietnam: https://en.wikipedia.org/wiki/Edward_Lansdale#Vietnam