Yeah. So when he made the accusation, it was just some faulty memory on his part, even though no one is debating that 1) they fucked and 2) that they started seeing each other when he was 16. That's the ticket. I mean, he went through the trouble of making the accusation to begin with for... no reason whatsoever, apparently. And after doing it for no reason, he was like "oh damn, my bad!"
And yes, I'm sure he was terrified that his allegedly false accusation was a lie. Even though it's absolutely nothing but a he-said/he-said situation, and the only thing that would need to really be proved is that they were seeing each other when he was 16.