1: don't use "snapchat" if you want security. this comes accross as one of thiose ridiculous ignorant comments from people who claim they'll only use Apple device, while they share all their information on social media.
2: this has nothing to do with the OS and are App specific restrictions. There is nothing stopping me today on going into any snapchat I have, and taking screen shots. this isn't something Apple is currently protecting you from.
I have only seen OS's protect content of apps when specifically under a managed solution that controls such access. For Example, I have outlook MDM'd on my corporate network. Users can load their outlook on their phone. but you cannot screenshot it as the app will only look blurry to all external programs. You cannot copy and paste between the apps either. This isn't specific to an OS. this behaviour is true on both Android and iOS and is a feature of the applications themselevs
honestly. Peopple need to learn exactly what Apple security is that they're being sold. You are NOT having your in-app content protected from 3rd party services by Apple's rules. As long as you are relying on someone elses servers and applications, you are theoretically at risk.
Even today, you need to assume that no communication, even with iOS users is "safe" u nless you are using a toolset that guarantees that there is no way of screen recording or taking images of your devices display.