The in flight entertainment system does not have any link to the flight control system..........end of conversation. It does receive selected information from the Inertial Reference System to enable the moving map display.
Also, having replaced hundreds of seat electronic boxes, I can also tell you that sitting in a seat and bending down to fiddle about with one is an impossibility unless you are an Olympic class contortionist and even then you are going to have to be greased up. If you want access to one, the general procedure is to lay flat on your stomach, shoe horn yourself down between the seats, legs out in the isle, sweat a bit, use some adult words and get on with it. Now I am pretty sure this would not go unnoticed by the trolley-dollies or a myriad of passengers with smart phones who would have loaded this spectacle up to social media sites. I am calling BS and publicly calling him a liar................!
Also
A cybersecurity analyst who was removed from a United Airlines flight after tweeting about the airplane's security vulnerabilities told an FBI agent he had previously hacked into the in-flight entertainment system on a different flight and was able to take command of the plane long enough to make it fly sideways.
Unless he has also reprogrammed the laws of physics with his laptop too, as far as I am aware (after 30 years in aviation), aircraft don't fly sideways........?