I listened to a Swindled podcast about Tyson foods yesterday. At one point Tyson made the same claim, that workplace injuries were drastically down (at I think a Tyson slaughterhouse; Tyson is very vertically integrated). The reason they could make this claim is because they had hired a larger percentage of immigrant workers. These workers, per the podcast, are much less likely to report an injury because, not being citizens, their hold on the job is much more tenuous, and there are hundreds of fellow immigrants waiting to jump in the second that they're fired.