I think that the article is referring to Kerry's grandfather when it says "Gundacker said he is '1,000 percent certain' that Kerry was born to a Jewish family."
In other words, you are right about John Kerry, but Gundacker is right about Frederick Kerry.
Indeed, master brewer or not, had the grandfather been baptized and had he and his progeny remained in Czechoslovakia, Moravia or Silesia, all would have been thrown in the concentration camps for being Jews, including John Kerry (Kohn)who at that point was 1/4 Jewish easily a qualifier on the Hitlerian 1/32 test for the gas chambers.