How does Maupassant's short story "A Duel" end?

Guy de Maupassant's short story "A Duel" ends with profound irony.

Throughout the narrative, the reader perceives the Frenchman as repressed by prudent passivity and "sorrowful resignation" because of his country's occupation, while the Prussian officer is obnoxiously aggressive as the victor, boasting of the Prussians' conquest of French towns. The two Englishmen on the train with the Prussian and the Frenchman seem indifferent to either of the opposing countrymen.

However, the Englishmen, "impelled by curiosity," do observe the interchange between the Prussian officer and M. Dubuis after the Frenchman has refused to comply with the order given him to buy the officer some tobacco when the train stops. This refusal develops into a fight in which the infuriated Dubuis proves the victor as he uses his weight to hold down the hated Prussian and beats him "without taking a breath or knowing where his blows fell." 

After receiving this beating, the officer demands satisfaction, challenging Dubuis to a duel: "Unless you give me satisfaction with pistols, I will kill you." Although he has never used a pistol, Dubuis defiantly responds, "I am quite ready." Then, he asks the Englishmen if they will be his seconds, and they readily agree. The train stops and the officer finds two comrades, who loan him pistols.

As they stand by, the seemingly indifferent Englishmen constantly regard their watches, lest they miss the train. When the signal is given, Dubuis fires rapidly and at random, somehow managing to kill the obnoxious Prussian. One of the Englishmen expresses his delight, exclaiming a simple "Ah!" The other, still holding his watch, grabs the Frenchman's arm and the two hurry him in "double-quick time" toward the train station with his elated countrymen running alongside their hero. As the train begins to move, the trio leap into the carriage.

Then the Englishmen, taking off their traveling caps, waved them three times over their heads, enthusiastically exclaiming:
"Hip! hip! hip! hurrah!"

They shake the hand of Monsieur Dubuis. Finally, these men, who ironically have been the secret allies of the Frenchman all along, return to their own private corner in typical quiet British restraint.