strange 666 appearing in Revival

while reading revival I stumbled over this .666. at the end of the paragraph in the photo (appears in chapter IV). it really irritated me because it has seemingly no connection whatsoever to the text surrounding it.

I proceeded to finish the book, wondering if it would possibly resolved within the story, but coming back it's still quite odd to me.

does anyone know if there is an explanation for the appearance of these numbers in this particular place? or is this maybe even a printing mistake?