Well the thing to note here is that "grift" is a count noun. (Their definitions as verbs is not what's relevant here!) You can't say "grift is occurring here"; you can say "a grift is occuring here". Meanwhile, "graft", in the sense of the abuse of an office for personal gain, is a mass noun. Perhaps the commenter's mistake was leaving out an article rather than using the wrong word? The latter seems more likely to me, however.

No, it's not. "Grift" is a count noun. You can't say "grift is occurring here"; you can say "a grift is occuring here", or "grifts are occurring here", but not just "grift is occurring here". Meanwhile, "graft", in the sense of the abuse of an office for personal gain, is a mass noun and can be used this way. Perhaps the commenter's mistake was leaving out an article rather than using the wrong word? The latter seems more likely to me, however.