Apple Core Media includes iOS devices, the podcast app and HTML5 media players in Mobile Safari Smartphone apps.
Whenever someone downloads a podcast Megaphone receives a request in our logs and part of that is called a "User Agent String" - this can include which application is being used to download the podcast. A good chunk of the time we get "Apple Core Media." The only thing you can know for sure is that the download has happened on an Apple device. We aren't able to distinguish if it's a phone or a laptop and we can't tell if it's an Apple software or if it's another developer's app that is using the Apple APIs.
Though we can’t say with certainty, it’s safe to say that the majority of the Apple Core Media downloads are coming from the default Podcasts app on iOS devices.