If you want to get really pedantic those are screenshots in the app drawer that are swapped with an application's surface in SurfaceFlinger just as it comes fullscreen.
But yeah, Android doesn't kill apps outright when you switch away, that would be a pretty poor experience to restart each time you opened a link in Twitter and came back from it for instance.
Re:A JVM Does That? (2011) [pdf]
by BinaryIdiot on Thursday July 07, 2016 @08:46PM
(#12052999)
> if you want to get really pedantic those are screenshots in the app drawer that are swapped with an application's surface in SurfaceFlinger just as it comes fullscreen.
Oh I know I was just being specific since you said they were "just" screenshots. Wanted to make sure it was clear some of those apps may in fact still be in memory. ️
That's not entirely accurate. Many of the apps can and will stay in memory (it doesn't suspend all of them). Not that that's necessarily a bad thing.