I don't think there is anything weird regarding the cause of death listed on Murray's certificate. When the headbone breaks, doctors call that a "skull fracture". Of course, it isn't the skull fracture per se that's the problem -- it's the injury to the underlying brain that kills you. Ouch.
When a person dies, the cause of death is either determined by the circumstances and the outward physical signs alone, or that plus an autopsy, in which the coroner cuts them open. Most of the time a cut-them-open autopsy isn't needed or appropriate. The important point is that in the absence of an autopsy, you have a doctor making an educated guess which may or may not be accurate.
I looked hard at that Murray certificate. I can't tell if an autopsy was performed, but I doubt it. If that were the case, I imagine the doctor would have described bleeding in the brain (eg. "cerebral contusion" or "cerebral hemmorrhage", etc) as the cause of death. But the whole thing seems pretty much in order Linda.