He hasn't the faintest idea if any of that's true, but it sounds plausible.
"What were you going to have me believe if it'd worked?" she wonders.
"So you were going to have me think I'd seen you cast a Patronus and hold off the second one till I'd finished off the first?" she wonders.
"Makes a much better story, doesn't it? You're casting Silverlight- surprised from behind by another Dementor!- and then I heroically fend it off!"
"If we go back with conflicting stories Hermione will believe me, and she's even more famous than you are, now. Do you think we can agree on something, or do you want to find out who's more credible, you or Hermione Granger?"
"I do still need somebody to find Dementors for me to kill and take me to and fro because I'm eleven. I obviously don't actually need anybody protecting me from them, just somebody who's more than seventeen years old. Are you going to keep helping, or are you bored now you know you can't Obliviate me, or do I have to worry about you casting other spells on me, or what?"
"Then maybe we have a deal. How about you encouraged me to try having both Patronuses out just in case that would work, and I tried it before we went into the woods and wouldn't you know it worked fine, and two Dementors weren't a problem and you never had to cast your own to begin with and you're very proud of me."
"Okay. I'm probably going to stick to the literal truth, but I don't have to mention everything or tell it in the right order. And that can be the implication. As long as you don't get on my nerves." Pause. "Memory Charms - on anybody - get on my nerves - and now I know that you're still the sort of person who wants to cast them even after all that time in the hospital. But if you stop -" She shrugs. "Then I have better things to do than try to punish you."
He doesn't think he can get away with pretending to be going on separate adventures while simultaneously chaperoning Silverlight after Dementors; he doubts this will lose him any fans. As nearly as he can tell, most of the wizards who would go on story-quality adventures have been wrapped up in the war for the past few years; he'd have little material in any case.
"Okay. We can go back to Hogwarts then. How did you find the place?" she asks, keeping hold of her chimaera wand but starting back towards the broomsticks.
"That makes sense, since that way we could fly. Er - you can actually Apparate? Right?"