It was designed so that if someone were to run for the presidency, he’d have to resign from the governorship, and DeSantis’s people seem to read it that way. But “nominee” is not a public office; DeSantis won’t have to resign until he wins and accepts the nomination.
Perhaps you read the law differently but it does not have to be a public office. Once he declares or officially files for the Primary, he has to resign if the law is not changed by that time.