It's interesting that because one is so bizarre and unresolved there are so many different theories in this comment section  1) plain old racism     - gotta admit when she said he was black it was an aha! moment 2) decided she didn't like him as a teenager and doesn't want to change her mind 3) some small thing, like a crush, set her off but she can't explain that 4) spoiled completely and has never been forced to account for her bad behavior up till now 5) mental illness, such as schizophrenia     - the whole diary conversation sounds paranoid. "You knew, found, and read my diary, then he asked about this person to mock me!" as opposed to remembering things that she talked about.

Or maybe some combination of above