Even if he knew, saying that would be a good way to try to get Harry to reveal something. What he would have heard from Draco is that Harry has a super-bright Patronus whose form he keeps secret; he would be curious.
So I don’t think this quote is strong evidence that Lucius hasn’t heard about the Patronus from Draco, since it is pretty likely that he would say something like this even if he has.
EDIT: Actually, since he believes Harry is Voldemort, he probably thinks the Patronus light he showed Draco was an illusion, and not useful for getting out of Azkaban at all. If he thinks Harry is Voldemort he’s unlikely, then, to pry for information about it in this way.
Even if he knew, saying that would be a good way to try to get Harry to reveal something. What he would have heard from Draco is that Harry has a super-bright Patronus whose form he keeps secret; he would be curious. So I don’t think this quote is strong evidence that Lucius hasn’t heard about the Patronus from Draco, since it is pretty likely that he would say something like this even if he has.
EDIT: Actually, since he believes Harry is Voldemort, he probably thinks the Patronus light he showed Draco was an illusion, and not useful for getting out of Azkaban at all. If he thinks Harry is Voldemort he’s unlikely, then, to pry for information about it in this way.
Also, Draco may be more inclined to separate his observations from the implications of his observations. He’s a scientist now, don’t you know.
That may provide Lucius with superior intelligence, relative to what he would otherwise have obtained from a child raised by a doting Darth Vader.