Techland made a build of Dying Light exclusively for YouTube star Pew Die Pie, which seems rather generous but he has returned the favour by offering the quote which is used for in-store advertising of the game, presumably created by the publishers, Warner Bros.
The video from which the quote has been taken from is sponsored by Techland and you can hear Pew Die Pie screech it at around the twenty second mark.
So to recap, a build of the game made exclusively for Pew Die Pie – though similar preview builds were made available to press – on a video sponsored by Techland is the source of the quote used in the advertising.
As a separate point, there have been no reviews of Dying Light as Techland did not send out review copies until twelve hours before launch, which prospective buyers will be particularly wary of after the fumbled game releases of late last year.
Update: Edited the last two paragraphs for greater distinction and clarity.
Thanks to Hardcore Gamer for the image.