The info has been hinted at for a long time, PETA's just the group who stuck their neck out. Not many others have bothered to speak up - why should they, PETA's taking the flack. Humane societies and other advocate groups receive donations from Iams/Eukanuba and other pet food manufacturers. Think of it as old fashioned hush money. Eukanuba sponsors quite a few dog sporting events and dog shows. Most groups are too smart to bite the hand that feeds them. I kind of get a kick out of listening to the dog owners and trainers talking about nutrition at those things. They all very carefully do NOT say that they feed their dogs the sponsor's products!
If you look at it using common sense, Iams and Eukanuba aren't the biggest producers out there. If PETA were going to manufacture evidence, why go after one of the smaller fish when there are several other, larger ones? Their pattern has always been to single out the most egregious, dramatic example they can and use it to shake everyone's cage.
PETA has been taken over by the fanatics, but once upon a time they did do a good job of bringing things to the attention of the public. Like too many groups, though, they just got totally subsumed by the crazies in their midst.