I agree that they should have stated that they worked on the game when reviewing it, but gamespot is just overreacting. A few people who worked on the game reviewed it giving it perfect scores. Players reviewing games are just opinions, sure its from someone who worked on making the game so their opinion is probably biased but is it any different than someone who hates adventure games and gets on there to rant on how much it sucks giving it a 1?
Its not as if telltale created hundreds of accounts and spammed the site with hundreds of perfect reviews. That would be cause for getting this upset over it.