The full civil code text applicable for every date since at least 1817 is available at Legifrance.gouv.fr[1] so I suppose he just wrote a parser to transform each of these pages into plaintext, another one to get a list of all amendments, and commited each different version.
The author mention he did it in an afternoon of code, so it's definitely not manually generated :
"Voici un petit hack, résultat d'une après-midi de code"
I do agree that the technical details would be interesting.
[1]http://www.legifrance.gouv.fr/affichCode.do?cidTexte=LEGITEX...