That's by design and standard iOS behaviour (it has been there for years). Tapping anywhere on the system toolbar (i.e. where the clock, wifi, signal strength indicators are) brings the main scrollable view to its "topmost" position.
I really dislike behavior like this that is useful to a few people but is far more likely to be encountered accidentally and feel buggy.
The only disadvantage is that many users do not know about this feature (because there is no indication that the status bar tab is supposed to do something like that) which is the reason many use think an app is buggy after they have tabbed on it accidentally.
Precisely why this behavior should be considered unfriendly. It's not intuitive and is prone to accidents by the vast majority of the target market.
Even just making it a double-tap would make it drastically better, and double-taps are closer to convention as well. Double-click the left or right arrows in an overloaded tab bar in Firefox on desktop, for instance, for it to scroll a full row over.
I've noticed that most people find the feature accidentally, but then once they realize it's an option, use it extensively.
WhatsApp shows a small button in the lower-right corner once you scroll up a few messages for this purpose. iMessage scrolls back to the bottom as soon as you focus the input field. I don't know about the others.
But yeah, it highly depends on how the developers decide to implement it, which is suboptimal :(
I thought this was one of Apple's "protected" features that everyone used/loved - guess not!
Seriously, try to e.g. delete an email from the system's mail app, then vigorously shake your phone in anger. A popup asking you to "Undo delete" should appear on the screen (Many applications hook into this seemingly standard undo mechanism on iOS).
Some things in iOS are objectively weird and unintuitive but I miss them so much whenever I use an Android phone.
"You appear to be shaking your phone in frustration. Would you like to un-delete that?" :)
What's two flicks got that this doesn't? Or maybe if a shortcut was desired for extremely long views, why not make it a double tap?
Try 4-5 (or more) flicks and you also have to wait for the scrolling to happen (at the speed of your flick) .... contrast that with one "press" on iOS - it's not even close - I use the feature daily.