Strictly speaking, it’s the speed of light in a vacuum that is the absolute; the speed of light decreases in anything other than a vacuum (the origin of diffraction effects at air/water interface) and in fact Cerenkov radiation (the blue glow (NOT green!) arising from used nuclear fuel stored under water) arises from high energy beta-particles (electrons) exceeding the local speed of light (ie. in water not vacuum).
It is likely that there is a systematic basis for the apparent observed neutrino behaviour in this case; if Einstein’s General Relativity is proven not to apply in this instance it will be a significant revelation. Having said that, there is a long running breakdown between general relativity and quantum mechanics which has yet to be explained (string/membrane theory attempts, but is very hard to substantiate in any meaningful sense) and the greatest strength of the scientific method is that any theory can be proved incorrect…