WTF? I just got 2 down votes for this? It was a serious question. I want to know, did they take a negative measurement too, and if they didn't, how does this prove relativity?
The experiment set out to experimentally test the accuracy of Einstein's predictions. The results of the experiment showed that under these specific circumstances, the predictions line up extremely well with observations.
There's no "control group" for this kind of test. Of course, they could potentially run multiple experiments to verify Einstein's predictions under different circumstances. That might provide useful information, but the lack of such information in no way discredits the results of this particular experiment.
If you want to read more about the experimental protocol, check out the final results paper: http://arxiv.org/pdf/1105.3456v1