The article's focus on a relatively marginal point -- the history of the five million number -- is inappropriate. It looks like an attempt to distract the reader from actual human suffering, and to trivialize that suffering by casting doubt on the number of victims. If part of the story is made up, maybe the entire story is made up.
What is needed is a recognition of these victims and a full humanity brought to ways to discuss these victims, while also recognizing that Jews were victimized by Nazis in ways that others were not -- a larger percentage of Jews than of any other group were murdered.
A neo-Nazi website I would prefer not to link here addresses the JTA article and says, paraphrase, see, the Jews are admitting that they made up the five million number just to get sympathy for Jews. No doubt they made up the six million number, too. This is unfortunate.
Neither number is made up. Both numbers reflect real history. The Wikipedia page on victims is here.
The USHMM's numbers are here.
Wikipedia attempts to chart deaths as you see, below.