I contacted the Raoul Wallenberg Foundation. They in turn contacted Prof. Alberto Melloni who they said and I quote (actually cut and paste) " “THE” authority in this matter." His response was that this quote COULDN’T be confirmed: Here is his response (keep in mind that English is not his first language):
No: it does not belong to the “written Roncalli”; the language is a post-Vatican II language. The mood of Roncalli was much more subtile: and the Jews (only the Jews!) were able to discern it because they know him from Turkey and from France as a friend. Just as piece of evidence one must recall that the first gesture of friendship of Pope John XXIII was in front of the Great Temple in Rome: on the shabbat he asked the chauffer to stop the car and he blessed the Jews. Of course he blessed them with the Sign of the Cross, that was a gesture very ambiguous for the Jewry. But everybody captured the blessing as such, and they were happy (rav Toaff gives a moving account of this). This explains that Roncalli did not use very outspoken ant-antisemitc language, but small wards and things that made clear his positiion. Alberto Melloni
As far as I can tell from my research is that it was conceived by some dissident Catholics (and anti-Semites) to “prove” that Pope John XXIII was an anti-pope. It then took on a life of it’s own and got passed around the Internet as valid by unsuspecting people (even many reliable, well meaning ones). Much like “Columbus thought the earth was flat”.
I think it’s important because everything a Pope says can be twisted and used against the Church. It is hard enough defending the truth without having to make sense out of misstatements.