Also, the author is French.
Yes. One thing that did occur to me as I was writing my first post is that French usage in this matter (I'm not aware of international variation) seems to be closer to the "British" than to the "American."
I don't know just how much influence that fact has here, though. In other words, maybe French usage influenced him to choose the British style, maybe he meant to use the American style but used something closer to French--or maybe his French background didn't matter much here.
My main message (directed not mainly at you but in general) is broader than his example:
Placing the period outside quotation marks does happen in respectable English-language writing in other countries. Someone from Britain may even wonder if the American style is "proper." I tend to use the American style simply because it's what I know and most of my readers know; I've heard the British style called "more logical," and I can see why.