It lost any credibility in the very first paragraph.
Originally Posted by OP
A poster claiming to be a games journalist for "a Playstation magazine in the UK" (presumably PSM3) has professed, on the GTA Forums, to having privileged information about the game. He says that magazine staff experienced 30 minutes of Rockstar's Grand Theft Auto V at the developer's Scotland offices.
Nothing works like that. What would Rockstar achieve by giving journalists a sneak peek at the game if they weren't writing articles about it for advertisement? Journalists don't do anything other than promoting, and if it was for promotion purposes there would have been articles popping up on all the major games websites as each journalist rushed together an article to publish first.
The post might be a good read, but it's nothing but some random fan's ideas.