What is ironic about the doctor's reaction to the lieutenant's wounded arm in "An Episode of War"?

The surgeon is very dismissive of and unconcerned about
the lieutenant’s wound, and seems irritated that the man has brought him more work to
do. He treats the officer as though he is a child crying over a scraped knee, though the
lieutenant is being very calm and unobtrusive about the whole situation. As the surgeon
is directing the soldier to the hospital tents, “His voice contained the same scorn as
if he were saying, ‘You will have to go to jail.’” Here is one sense of irony—a doctor
treating an injury as if it were a criminal offense, and the injured as if he were
guilty, rather than a victim. The greatest irony, however, comes when the lieutenant
wonders placidly whether his arm will be amputated. The surgeon huffs contemptuously at
this suggestion, and exclaims patronizingly, "Nonsense, man! Nonsense! Nonsense!...Come
along, now. I won't amputate it. Come along. Don't be a baby." But, Crane notes shortly
after, “this is the story of how the lieutenant lost his arm.”  The surgeon dismisses
the officer’s wound and acts as though he were an ignorant child for even mentioning
amputation, and yet amputation is the arm’s ultimate fate.