Like you said, it was a nice touch, of course it was, it was meant to be.
It's because this anecdote is from the book "Mémoires de Sanson, pour servir à l'histoire de la Révolution française" written by various novelist ( the main author is Louis-François L'Héritier in case eveyone was wondering, i doubt you'll find a lot a of stuff about him even in french, but Honoré de Balzac, a really pretty famour french author also worked on it, ) and i dare to assume that the mangaka used this as reference for the story.
"Memoire'' sound like an autobiography, but it's not, because the book was published in 1830 and Charles-Henri Sanson will die way earlier ( don't be shocked, it's not like he was supposed to be in his fifties went Louis XVI was executed) , and like i said, i wasn't written by a Sanson familly member but by Novelists.
And Novelist loves to write about emotionally charged stories just like we like to read them.