The short answer to your question is that he lied to her.
The longer answer is that the entire thing was so full of lies, from side to side, top to bottom, inside-out, and all around.
First off, let’s look at the lies from AP. She lied to him about who she was, entirely. She talked the way she did because she knew he wanted to hear the things she said, NOT because the things she was saying were necessarily true. She was saying things in order to have sex with your WH. That was her purpose. And don’t think anything else, because that is the reason she said the things in the first place. She had zero consideration of you or his marital status - it was what SHE wanted. So she lied about who she was, what she liked, what she didn’t like, and just about everything, in order to attract your WH.
Your WH lied about himself to her. He likely told her things that were just dumb. White lies about liking what she was wearing, or movies she said she liked when he hated them, etc. It’s just how this works. He lied about compliments he gave her, when his intention was to have sex. Lies.
He told her lies because he wanted sex. He lied so she would consent. He lied so she would feel good, and play along, and she lied so he would continue.
They lied so the excitement would rise. They lied so the secrecy would play on, because it was tantalizing. They lied because it’s part of what makes an affair lust seem so much more than what it is, and it feeds on itself.
He said things because they worked for what he wanted, which was to keep having sex, to keep the level of interest up for her, to keep that sense of "newness" going - because in fact, the ONLY thing true here is that he was after some sex that was "new", and in fact this AP could have been anyone anywhere on the planet, she was not special at all. Nothing in this affair was actually about her. It was all about your WH.
And he lied to and about you. Lied to her about you, so she she would believe things about your relationship that would make her feel more comfortable engaging with him. Lied to you about where he was, what he was doing, and how he felt during the affair.
But what he just said about not being in love with her? That’s the one thing that rings true here. His words sound real, because they are in keeping with the idea of affairs for the sake of sex and not for emotional connection.
(If he thought he was in "love" but suddenly snapped out of it, he could have been feeling limerence. Hard to say.)
But it sounds like he’s now giving you some really hard truths. What’s harder is trying to make sense out of something that really doesn’t make sense at all - which is where you are right now.
My heart goes out to you.