Look, it's all regional and cultural and there are a million names for a bread roll and no-one has the right to judge and everything...
But someone said on another thread that a fairy cake with no icing is a bun (I mean, no, but let's go with it) and a currant bun is part of a different related category - the "sticky bun".
And also included in sticky buns are... doughnuts and... apple turnovers.
So, sure, it's all relative and whatever but... an apple turnover is not a bun, right?