"It isn't a secret, exactly. I just can't explain how I do it."

Which was true, she could go into how there are Enlightened, and how they are more 'like Pokemon' than people who aren't. But that won't explain why she's more attuned to Pokemon than she is people, and why she understands them when they talk to her. And since that's what he cared about, that's what she can't answer.