Sorry, you've misread the page, it's actually claiming the exact opposite.

Etymology sections in dictionaries can be kind of confusingly phrased sometimes, so I'll break it down:

also goddamn, late 14c.

This means that the phrase "God damn" has been around in the English language since the late 14th century.

from God + damn (v.).

This means the phrase actually is, straightforwardly, from the English words "God" and "damn".

Goddam (Old French godon, 14c.) was said to have been a term of reproach applied to the English by the French.

This part is saying that Frenchmen supposedly corrupted the English phrase "God damn" into godon (and variants like goddam, goddem) as a derogatory term for Englishmen — apparently mocking Englishmen for being foul-mouthed or uncouth, i.e. that Englishmen say "God damn!" so often that it might as well be their name.

Hence French godan "fraud, deception, humbug" (17c.).

This is to say that that French-language derogatory term for Englishmen, about three hundred years after the phrase "God damn" first entered the English lexicon, came to take on a new meaning in French of "fraud, deception, humbug".