No, it's a launcher, not a app, the clue is in the name, launchers have different system rights and can implement things that standard apps do not have access too.
Right, because Retroarch has no idea that there is another app running that you want to return to, it is doing EXACTYLY what it should, quitting Retroarch to the home screen.
And don't you presume to think that i do not know what the Retroid Pocket is, or how Android works. Just because it is a physical button and not a onscreen one is of zero importance they both provide the same function, they return to the OS home screen by default, Can they be reconfigured, sure, is that a good idea, probably not, how would i get back to my actual homescreen on my daily phone that also has Launchbox on it for some occasional gaming if the home button just takes me to Launchbox?
You are confusing Launchers and Apps here, they are not the same thing, and despite the name, Launchbox is a APP, not a Android Launcher.