I don't see it often but one has to assume with how much the Giantbombing account is used from quicklooks to reviews and just personally, sometimes other reviewers playing multiplayer games are going to come across it. Which is why I found it hilarious when watching through Gametrailers Tron Evolution: The game review and they showed a snippet of multiplayer (maybe about 30 seconds of footage) the last snippet of footage has Giantbombing has Joined the Game shown. 
 
Not really much else to say besides the fact that I found it highly entertaining, especially considering you don't usually see reviewers interacting with other reviewers in multiplayer. Especially when one is recording game play for review and to see it displayed gave me a little chuckle.  
 
That is all.  

It's happened before in many different reviews.

its what they have to do so, yeah i would assume you would see other publications name in video reviews

Still pretty cool, though! :D

It's to be expected. Jeff knows plenty of people in the industry, so him joining the game of a fellow game journalist is no surprise.

" It's to be expected. Jeff knows plenty of people in the industry, so him joining the game of a fellow game journalist is no surprise. "

As far as pre-release, most people playing a game are developers and people in the press.