This is an incendiary and attention-seeking claim, with an eensy-weensy tiny kernel of truth to it.
The refugees from Turkey after 1922 (and that’s not just Pontic Greeks, but Western Asia Minor Greeks and Cappadocian Greeks too) were dispossessed and impoverished. They gravitated to the left and the Communist Party.
As a lot of dispossessed and impoverished people tend to do.
If some of them adopted communism so fervently as to become spies for the KGB, that would be plausible—but for the fact that the KGB was not called the KGB until 1954, by which time the Greek Communist Party leadership had been exiled to Tashkent, and the Communist Party driven underground. Would the Greek Communist Party of the 30s have loyally provided some intelligence to the OGPU, KGB’s predecessor of the time? I guess. And would some of them have been Pontic Greeks? I guess. *shrug*
Which is as polite as I can be about this question.