dungō

Because there is no way it can descend from the older High German forms.

But even the entry of german 'Dung' says : "From Middle High German tunc, tunge, from Old High German tung, tunga, from Proto-Germanic *dungō ". So this page is wrong and must be corrected ?

Indeed, that's wrong too. There's no explanation of why German suddenly got a "d" in the word.