What the two platform styles change
iOS and Android draw a notification differently, and the differences are what make a mockup read as one or the other. On iPhone the app name sits above the title in small capitals, the card corners are tighter, and the app icon is a rounded square. On Android the app name sits inline with the timestamp, the card is more rounded, and the icon is closer to a circle.
The platform control switches all of that at once, so you are not left adjusting details by hand. Everything else, the app name, title, message, time and icon colour, is yours to fill in.