Lung fever= pneumonia. The interesting thing about the use of this term, it is usually a term used by vets or large animal doctors to differentiate acute lobar pneumonia from catarrhal or bronchial pneumonia. It is a generalized disease that results in consolidation of one or more lobes of the lung. What this tells us about his death, is he was likely being treated by one of the numerous horse doctors (not a disparaging term in 1860's) who was smart enough to actually listen to his patient breathe and pound on his chest to make the diagnosis. Many poor soldiers were just listed as getting camp fever or some such none descriptive term. So what I'm trying to say is he probably got better than average medical care for the time just because the cause of death is more definitive and indicative of someone really interested in making a clinically significant diagnosis. Sad part is it was probably curable with 3 - 5 days of penicillin which we would wait another 80 years for.

FWIW
John R