This bit of the story hit me with so many 'this shop isn't actually here' markers that I figured this was a restless spirit trying to do restless spirit things when Flandre talked with M. Constantin about learning how to make stuffed animals. The 'proud craftsman desperately wanting to pass on their skills to a worthy heir' angle was clear when he handed off his tools to Flandre.

It's a well crafted bit of story, properly foreshadowed between the proprietor's physical age, his implied birthdate (somewhere in the 1850's, or 90 years before the story takes place) and his apparent lack of care for material compensation.