While I did miss that point specifically, I still think the fact that most people aren't aware of how long phones are "supported" (which can mean a few things itself) is relevant. Since most people aren't aware of that, I doubt it factors into whether or not they pass the phone down. Certainly not to the level that it would affect these numbers. They're just going to care if it works or not.... unless the kid says they don't want an Android phone, then they decide whether that's too bad or to go ahead and get them an iPhone.
The bolded was specifically the point so I'm not sure how this was possible.
People aren't aware 'iPhones are supported for another 5 years therefore I'll give my kid my iPhone', but people are aware 'my phone still works, gets new features, and apps on it still work, so I'll give my kid the phone as it's good enough'.
The phones having long support aids in the value in the second-hand market being sustained, increasing the likelihood the phone gets recirculated (and then used) rather than just discarded; this increases the likelihood of handing it down and the likelihood of it being resold. This makes 'old' phones still perceived as still being valuable/usable to teens, rather than just 'old'/'worthless'.
The prioritisation of app development on iPhones is relevant because it means even with older, cheaper phones teens are still able to use many of the latest features on their favourite app whereas those features may not be prioritised on Android phones; Snapchat for example allowed the addition of music to Snaps on iOS far before Android supported it. Kids don't know 'this app's development is prioritised on iOS' but they do know 'I can add music onto my Snaps on iOS but not Android'.
We know explicitly the volume of iPhone sales is outpaced by the share of iOS usage, and that's a clear indication of how they're far larger factors than 'its a status symbol' for a teenage market which largely can't afford to self-purchase the latest devices but absolutely can afford (and are willing to get) older models because they still get the features their friends have (or alternatively they'll purchase a new model and then hold on to that for a few years).