Your count here relies heavily on the 2-3 million Poles, but to the best of my understanding, those were killed in war, either during actual battle or during the Wehrmacht's pillage and destruction. I say that because, according to the article, only ("only" ... yeah) 0.5 million non-Jews died in concentration camps:

> While as many as 35 million people were killed overall because of Nazi aggression, the number of non-Jews who died in the concentration camps is no more than half a million, Bauer said.

... so I can't see a way to reconcile that with the figure for Poles except by considering them overwhelmingly casualties of war, not a policy of extermination.

And so, as far as I can see, the original article is broadly right and your comment is inaccurate.