Facebook now performs attribution based on users and not devices.
This works by Facebook identifying users based on their Facebook account. Some users have both iOS and Android devices associated to the same Facebook account.
If such a user clicks or views an ad for your app on their Android device, but install the app on their iOS device, Facebook considers themselves as having generated the install. As a result, an Android Campaign name appears on your iOS dashboard.
Mr A. Flyer is busy on his Android device. While using it, he clicks on an Android Facebook campaign advert for an app called Bubbles. He does not download the app.
One day later, Mr Flyer decides to download the Bubbles app organically on his iOS device and launches it.
In this situation, AppsFlyer attribution takes the Android Facebook campaign from Facebook and presents it in the iOS Dashboard where Mr Flyer downloaded and launched it from.