I don't know. It can not be that big to the French anymore. Maybe some typical national BS.
We Germans had also a strange party with a corpse some years ago. I am talking about the Prussian Friedrich II of Prussia, whose coffin was taken to the Swabian castle of Hohenzollern in the last days of WWII. His last wish was to be buried quietly together with his dogs at midnight without any audience in the garden of his château Sanssouci in Potsdam. Since he was one of the most important leaders in the Prussian history his wish of privacy was never respected. It seems that a royal corpse still has its political importance.
Our former chancellor Helmut Kohl took the coffin from Hohenzollern on a gun carriage to bury it with a big millitary tattoo and lots of Dschingderassabumm in Sanssouci. The "Frankfurter Allgemeine", the most important newspaper in Germany called it "Umtopfung" (repot in reference to changing pots of flowers) back then.
BTW - I also had my relationship to this corpse and coffin. When I was a kid (already 17 years old) we made a funny vampire film in the castle of Hohenzollern during a school project. Since the Hohenzollern was nearby and we all knew the staff in the castle we were allowed to use it for the film. As you might imagine it was a quite funny time. Nice girls and lots of party. Anyway once we were alone with the coffin of Frederic and his Father in the chapel of the castle we could not resist to lift the coffin on one side. I still can remember the rumbling noise the skull made when it was rolling to the other side of the coffin. Poor Frederic!
Today I would not do such disrespectful BS anymore of course but back then it was ... ...a age-related necessity.
You see - never leave teenagers alone. Either they start to kiss, to drink or to roll skulls. ;)
Castle Hohenzollern. The coffin on the right side was the one of Friedrich II (the great) the one on the left from his father Friedrich Wilhelm I.