Jon Lansman switched horses 4 years ago - and stepped down as Momentum chair 3 years ago. He has been on a rapid journey to the right and has embraced Zionism. His comments are no surprise.
I don't think it has much to do with him being Jewish. He says he is an atheist - but politically he has got into bed with the JLM (the pro Israel/Zionist group in Labour - made up of Jewish and non Jewish members) and denounced the JVL (the anti Israel/Zionist group in Labour - made up of Jewish members).
Lansman is beginning to sound a bit like John Mann, John Woodcock (the link above) and Ian Austin - all non-Jewish cheerleaders for Zionism and apartheid Israel. There are tens of thousands of UK Jewish people who disagree totally with them - and have taken part in the Palestine demonstrations and in many cases have chanted 'From the river to the sea' and know it is an anti-racist chant, not an anti semitic one.
Meanwhile in Gaza and the West Bank the bodies continue to pile up whilst most of the world watches. At least some are prepared to take a stand for peace and justice - whatever their heritage.