The "imposter" of "imposter syndrome" believes others didn't figure what they really are, that they're flawed, underskilled, will fail, etc. ; and that makes you somewhat of a fraud, i.e. an imposter, because they're secretly not the skilled person that was hired.
The "actual imposter" from the "imposter syndrome" would be someone who actually lied about their skills and flaws, or at the very least don't have these skills. I don't know if these "imposters" have the imposter syndrome or not - but for the sake of argument I would assume that they have the same doubts as everyone else and that they do have imposter syndrome.
The "actual imposter" who the author is mentioning is a con, someone who was secretly malfeasant and there for their own benefit. What's more is that from what the author is saying, they seem pretty skilled, and confident. So of course they don't have imposter syndrome: they fixed an organization, bring in money, their plan is going well.