It was probably good that Charlie grabbed her attention. He wasn't sure he wanted to explain anything in front of the kid; he wasn't entirely sure what might come spilling out once he started.
His immediate reaction was to want to defend the kid's actions. He wanted to say he was generally good for him, that it was probably more his fault than Charlie's - but he kept his mouth shut for now. Abi was trying to have a teaching moment, and he probably shouldn't ruin it.