While the story behind BccKing new owner may or may not be true, I would say that I didn't really got to see people "starting their journey" by telling they took over an account.
So I've seen it as a rather honest approach, hence my neutral feedback (since a warning is still in order there).

I don't like to apply the same rule everywhere, I prefer to think and take my own decision, case by case. And here it's.. fuzzy. Your negative feedback is not bad, and also not great either; although when you get such a strong feedback as you've got, you should indeed think it over and see if you did good. But it's your feedback and your decision.

I do agree that the new user should have made a new account. Clearly. But for the negative feedback you made... I expect you may get various answers, favoring your decision, or telling it was too harsh, .. or neutral. Again, it's your decision.