You know, back when I used to post on the UnrealMuscle boards, I would be hounded for suggesting that a lot of BBers took steroids.  It was like an elephant in the room, I mentioned the elephant and was made a bit of a pariah.  Sad as this is, I'm not surprised.  It's why I pointed-out earlier in this thread that, if BBing is ever to become anything less than a joke amongst the general public, they are either going to have to take this Belgian approach everywhere, or the governments of the UK and US will have to deregulate steroid usage.

When you mention NO2, do you mean a product brandname or the gas itself?

I think that NO2 was the brand name of the product, and that it was really NO, as AlexG said.  I just recall the claims they were making (about having perpetually 'pumped' muscles) and that "NO2" was emblazoned on a brochure in big letters.  It seemed designed more for show than for actual physical improvement.

I presume they were from the accrediting body?

As cpbell said, they are probably sent by whoever is sponsoring the event.  Then again, I would assume that this testing is in their rules and that the bodybuilders should not have been surprised, so perhaps some other governing body decided to make a random visit.  From what the article says, they've been tested before.  Lots of details are missing, so all we can do is guess.