It doesn't disprove any fact-checking articles, but, as a hypothetical example, imagine if you learned a fact-checker was convicted of writing lots of bad check

It doesn't disprove any fact-checking articles, but, as a hypothetical example, imagine if you learned a fact-checker was convicted of writing lots of bad checks. They might be perfectly honest in other areas of their life, but it creates a lot more skepticism, since you know they're willing to be dishonest in that one case. Plagiarism isn't necessarily as dishonest as financial fraud, but it's still a form of dishonesty and likely also intellectual laziness. Dishonesty and intellectual laziness are the opposites of what you want in a credible debunker/verifier, no matter the relevance or severity.