This is not at all sophistry, it's basic science. Experiments support or falsify because there are always an infinite number of other theories that can support any particular observation. So this muon experiment may support relativity theory, but does not prove relativity theory b/c there are other theories that can also explain these data. Just as with quantum theory, and the many different interpretations of quantum theory, there are in fact many different interpretations and approaches to the equations of special relativity (the Lorentz transformations), including the Lorentizan interpretation proposed by , er, Lorentz, which was quite different than Einstein's interpretation.