Late to the party, but here's one point of anecdata about a child who cut off her parents for no real reason:
I met this friend (call her Anna) in college. Nice enough person, ended up dating my then-bf's roommate, so we all spent a lot of time together. She was one of those people who loved to be "quirky", and she had a tendency for the dramatic, but not to any extreme extent.
Anna would always complain about her parents, and say that XYZ thing that they did was all because of being "overbearing" older, adoptive parents. But the stuff she would say was stuff like, "they called me to check in, like they do EVERY weekend". Stuff my parents, who were neither older nor adoptive, did all the time. Or, like "I was home for Christmas and they wanted me to wake up to go out for breakfast with them!". Yeah, admittedly annoying when you're used to a college sleep schedule, but not unexpected.
We've drifted apart since college, but we're still FB friends, and Anne occasionally posts stuff like "FYI, I'm not in touch with my parents, so if they contact you asking if I'm OK, don't tell them anything." While it's true that you can never know what goes on in another family, given her flair for the dramatic, if there was something else going on like abuse, I have no doubt at all she would've shared it with me.
I don't think Anne herself has any severe personality issues; I think she's just convinced herself that her parents are bad parents and proceeds accordingly.