That was my thought exactly. Then it occurred to me that an exploding star might actually have diverse points of origin as far apart as 0.9 light-seconds. If 7.3 billion light-years of travel is insufficient to create greater divergence than 0.9 seconds, we may have to wait for a much more distant event. My guess is that they decided that the noise of diverse points of origin sufficiently overrides the question of 0.9 seconds to the point that absent other evidence, it confirms rather than invalidates the theory of relativity.