glitch. that does not happen. you may have pressed something twice or did something else without your knowledge.
see if you can recreate it--you shouldn't be able to...
did you have any other background apps running (pandora, youtube, google play, etc)?
if you want to get back to an app thats running, thats what the pull down drawer is for. pull that down, then tap (once!) on the icon of the app you want to pull up to the front.