For want of a definite article, the meaning in Polish may have been more than slightly skewed. Undoubtedly, Gross issued his statement to the German press in EnglishLOL
One can read his original statement here: project-syndicate.org/commentary/eastern-europe-refugee-crisis-xenophobia-by-jan-gross-2015-09
Consider the Poles, who, deservedly proud of their society's anti-Nazi resistance, actually killed more Jews than Germans during the war.
If you click the link, the quote above has a link to an explanation which goes something like
"let us assume that 30,000 Germans were killed in Poland during the war by the Poles."
" The first killing spree [of Jews by Poles , in pogroms that accompanied the German attack against the Soviet Union and its aftermath in the summer and early autumn of 1941, amounts to several thousand victims.
...
According to estimates by Polish historians, about 10% of the Jewish ghetto population in Poland - some 200,000-250,000 people - tried to save themselves by running away from the ghettoes and hiding on the so-called Aryan side. Out of this population, about 40,000 Jews survived the war. The bulk of the Jewish population killed during this period perished either directly, killed by the Poles (or Ukrainians)
among whom they were hiding, or by being betrayed and delivered to German police outposts by the local population."
(I'd quote the rest but that would break the 100-word rule.)
With such damning facts, it's no wonder that some Poles want to take issue with what Gross didn't say than to address what he did say and what very much appears to be true.