Welcome to Android Central! It's not so much a default wallpaper as it is a way of preventing accidental touches if the phone turns on while in your pocket or in a bag. It sounds like you don't use a screen lock (which I would strongly caution against -- these days, there is so much sensitive personal information on your phone that it's always a good idea to set up a secure screen lock, whether it's a strong password/PIN or fingerprint) -- but even without a screen lock set, phones will still have this swipe-away screen that helps ensure you don't butt-dial anyone, or do anything possibly worse than that.
There might be some way to get rid of the swipe-away screen using something like Good Lock -- maybe @
mustang7757 has some insight into that.