Labour's Angela Smith said Mr Corbyn's attendance was a "blatant dismissal" of the case to tackle anti-Semitism in the party.
"Jeremy is a lifelong anti-racist and I think it came as a something of a shock to him to be described as being some kind of racist, of harboring antisemitic people in the party that he now leads", Lansman told BBC radio.
But Jewdas has been attacked by Labour MPs after criticising last week's Parliament Square demonstration against anti-Semitism in Labour, which was attended by dozens of MPs of all parties.
Speaking during a visit to Swindon, Corbyn said the event was "a celebration of Passover, which I celebrate with young Jewish people from my own community and my own constituency". "And he must know that meeting them now will give his members the message that the group's extreme views are ok".
The longtime leader of the Labour party tells Israeli TV that anti-Semitism must be rooted out "completely and totally". Blair said he is certain that the general British public is not at all anti-Semitic, and that Labor had to make it clear that anti-Jewish sentiment in party ranks can not be tolerated.
Following the letter, Corbyn said he was "sincerely sorry" for the pain caused and he plans to meet with Jewish representatives in order to "rebuild" confidence.
Nevertheless, senior leaders in the Labour Party appeared to have realized the damage the issue was inflicting, which may be why Momentum issued a declaration on Sunday acknowledging worries about anti-Semitism.
This comes after the Enough is Enough rally organised by the Board of Deputies and Jewish Leadership Council, where more then 1,500 people took to Westminster to protest against Labour anti-Semitism.
The group said: 'We are proud to be Jews and proud of everyone who attended, whether they were Jewish or not.
Amid the row, Labour's new general secretary Jennie Formby emailed party members to say she will use this week to "ensure the full implementation" of the recommendations of Shami Chakrabarti's 2016 report into anti-Semitism within Labour. "Isn't that a good thing?"
The London-based organisation describes itself as "radical voices for the alternative diaspora".
The decision to attend the event, which Corbyn's spokesman said was personal and not on behalf of the party, was branded "irresponsible and dangerous" by one Labour MP.
The spokesman also noted that Corbyn "wrote to the Board of Deputies and Jewish Leadership Council last week to ask for an urgent formal meeting to discuss tackling antisemitism in the Labour party and in society".
The chief executive of the Holocaust Educational Trust, Karen Pollock, said on Twitter it was "mocking and disrespectful".
In remarks that were implicitly critical of the Labour leader, Jon Lansman, the founder of Momentum, said this morning that the group's description of Israel as "sewage" was "not helpful" for efforts to tackle antisemitism within Labour.
Simply: "Great that there's so much interest in our work..."