It does not. They're not talking about hidden characters - they're talking about patterns in the distribution of letters or words, patterns that you would replicate if you retyped the output. Consider, for example, a pattern like "Sentences may contain only even numbers of seven-letter words." That's preserved if you manually retype, and it's even preserved through light editing - the edited output will no longer have 100% of sentences containing even numbers of seven-letter words, but it will have enough that having that many by random chance would be very unlikely. Note that this example is one that I just made up - what they're doing is presumably a lot more subtle.