Salam.
There is many month I have post one question to Islamic Centre for Research And Academics
They have respond me saying.
Assalamu alaikum wa rahmatullahi wa barakatuh,
Please excuse the delay in responding.
I will have to see the details of the particular narrative but shortly:
1. The sources are secondary and cannot stand against established evidence to the contrary which tells us that Umar (rA) nominated 6 people for the office of Caliphate after him and Ali (rA) was one of them. Therefore, even if the episode in the narrative is true it is clear that Umar (rA) did not bother much about it.
2. If the Jewish origins would have incited some hatred Ka'b would have hated Umar (rA) more as it was he who expelled the Jews from Khaibar (along with Christians of Najran) in accordance with the Prophetic directive.
3. Therefore, it is safe to conclude that the results brought out from the story are far fetched and at variance with established facts of history.
(Brother Waqar Cheema, Founder)