iOS standard behavior is for the label of the back button to truncate to "Back" if the label is too long. That may be why you are seeing this.
In addition, when a user navigates between articles in a collection the label will always be "Back". The primary reason for this was related to some assumptions about the length of article titles that led us to believe they would often get truncated to "Back."
ANdroid is different because there's a hardware button (always goes back to where the user tapped from) and a button in the Nav bar that goes "up" to the browse page (aka "parent" of the current view)
The next release of the iOS viewer will have some changes regarding the back button. Apple doesn't have a hardware button, gestures sort of take the place of that. The change we are making is to have bezel swipe always take the user "up" to the parent view (except at the top level, that brings up the menu).
We are also discussing additional design changes to handle multi-level navigation while maintaining simplicity in design (we want to avoid adding more and more navigation buttons to the view as the user navigates), plus additional linking behavior.