I think the graph shows the geographic extent of the languages not which language is primarily spoken in which region.
I was serious when I asked if this map was from 1750. It looks about right for that, at least for the western European countries whose history I know well. (I can only guess about all the ethnic pockets in Russia).
My guess is the author is assuming that everyone knows where the dominant, 'imperial' languages (English, French, German, Spanish, Russian ...) are spoken, and aims to represent the deltas from those. Either that, or it has an exaggerated anti-imperialist bias.