Your problem sounds like something is preventing the phone from even locking. I had a similar issue on my Galaxy S4. There's an app called Swann View Plus that I would use for viewing our cameras at work. For some reason, whenever I opened it, clicked back to home, and then locked the screen, when I woke up the phone I would not have to swipe to unlock, it would just be there at the home screen.
Now I have the same app on my Galaxy S5 and it doesn't do that, however I would look towards some kind of app causing this issue. Wipe your device to factory and check to see if it is still doing the same thing as it is now, or if it does as your friend's does which is also what mine does.
My Smartphone history with AT&T:
January 2005: Audiovox SMT5600 aka HTC Typhoon
June 2006: Cingular 8125 aka HTC Wizard
October 2007: AT&T Tilt aka HTC Kaiser
June 2009: AT&T Fuze aka HTC Raphael
November 2009: iPhone 3GS
July 2010: iPhone 4
October 2011: iPhone 4S
July 2012: Samsung Galaxy Nexus GSM/HSDPA+
May 2013: Samsung Galaxy S4 4G/LTE
April 2014: Samsung Galaxy S5 4G/LTE