Hat and Cloak uttered that line by way of drawing attention to the reason that blood-purists have taken her for an enemy (which is relevant because H&C wants to give the appearance of courting Hermione as an ally).
As an explanation of that hatred and danger it makes sense say it no matter who H&C turns out to be.
Hat and Cloak told Hermione “you are a Muggleborn and yet you possess a power of wizardry greater than any pureblood.”
Lucius can’t believe that. He can’t even afford for that belief to exist, so I don’t see him uttering it, even as flattery he “knows” to be false.
Lucius knows that his enemies believe muggleborn can be powerful wizards, so he can say that flattery to look like his enemies.
For people that believe blood has nothing to do with magic—they won’t state the obvious.
Hat and Cloak uttered that line by way of drawing attention to the reason that blood-purists have taken her for an enemy (which is relevant because H&C wants to give the appearance of courting Hermione as an ally). As an explanation of that hatred and danger it makes sense say it no matter who H&C turns out to be.