This may not be all that it seems - as several viewers have already pointed out, the camera angles and editing suggest multiple cameras that couldn't all be hidden. Nonetheless, if a dinosaur is running after you, do you care that some idiot with a camera is foolhardy enough to follow it? Maybe if you have time to think about it, but the best pranks take people by so much surprise that there isn't time to do so.
The fact that somebody created this fully realistic dino just to prank people in empty offices is the takeaway here. That person rules.
Video after the jump.