Yeah this article should be more forthright in describing meta-materials/left handed media. This media is highly dispersive and described by changes in constituent properties (permittivity, permeability) usually coinciding with frequency/wave propagation constant changes. From there we can describe the energy propagation via Poyntings theorem and this is no violation in a physical sense. This media is usually very complex/anisotropic and incredibly challenging to fabricate outside of a lab, wake me up when we can manufacture these /s