His being a "leftist" is irrelevant in this instance as it is not a defence against the charge that he deliberately uses language that refers directly to Germany's poisoned history in a context where he is critiquing current economic policy and influence.
If you had read all of the article you wold have seen that it points out that there are others who criticise German policy, that he's not alone in that regard - the point of the article is not to dismiss the criticism of German influence or to attack Mélenchon's own economic policies.
It's to highlight that he has, through the words he has chosen, shown a dislike and mistrust of Germans and a willingness to use history to amplify anti-German sentiment in the present.
I did not call him racist so do not put those words in my mouth.
The author of the piece did not call him racist so do not misrepresent what was written.