Do you not know how cheap good cameras are these days? and in all caps it says right under the video.
"THIS IS A NON-PROFIT FILM AND IS FOR PRIVATE USE ONLY NOT INTENDED FOR SALES OR COMMERCIAL USE. WE RESERVE THE COPYRIGHTS AND TM TO THE ORIGINAL CREATORS OF THE FOLLOWING CONTENT USED WITHIN THE FILM. THIS FILM WAS PRODUCED SOLELY FOR ENTERTAINMENT PURPOSES AND FOR THE LOVE TOWARD GAMING, MUSIC, AND AIRSOFTING."
I don't see anything wrong with that..
And one guy with a hobby of editing can put together all the sound effects straight from left4dead and put them into the video.