Specific electrochemical processes have their own characteristic photon emissions. Since there are some processes that occur distinctively in living organisms (e.g. to do with metabolism), it was previously thought that these would have characteristic photon emissions, but as far as I know these are the first observations of this kind of thing.

The effect changing with injury or anaesthetic I guess reflects the fact that there are different electrochemical processes occurring in these cases that have detectable differences in the photon emissions

I seem to recall the mechanism for anesthetics being something like temporarily depolarizing the mitochondrial walls to shut down ATP synthesis, so that might point towards where the effect is originating.