This is an interesting question about a convoluted comparison that seems to be open to interpretation. But it's also a much bigger question about a politician's views. I'll give my personal take on things as I try to guess Corbyn's intentions.
In a certain sense, there is an undeniable line drawn between Israel or the Netanyahu government and various self-styled Islamic states or organisations.
The Jewish friends are no more responsible, which I infer to mean "not at all responsible." For the sake of clarity, we can attempt to simplify the analogy:
Jews are not responsible for the actions of Israel or Netanyahu, in the same way that Muslims are not responsible for the actions of ISIS.
I think one can infer a connection between Netanyahu and ISIS if they choose to, but I don't think one has to read the connection as explicit. I think the negation of the association (not responsible for the actions) allows us to see the connection or not. If you think about it, a negation of association means that there isn't much of a comparison to begin with. It's a clever way to form an analogy, but in Corbyn's case, it has caused too much confusion.
So did Corbyn mean to call out Israel? It's no secret that Corbyn doesn't like Netanyahu politically. Corbyn is a progressive liberal, and Netanyahu is a hardline conservative who loves Donald Trump. Politically, they are opposites. And at least a few members of Corbyn's Labour Party have been accused of being anti-Zionist, while Netanyahu is the world's most outspoken Zionist.
At best, Corbyn was foolish to say something like this, because it has caused a lot of harm to his party. But also consider that a person can be a critic of Netanyahu and of the current governing party of Israel without being against the Israeli people. Indeed, one can be anti-Zionist without being anti-Semitic. Keep in mind, there is such a thing as anti-Zionist Judaism. There are valid ethical arguments both for and against Zionism. Corbyn insists that he is not anti-Semitic and that his party does not tolerate anti-Semitism, and from videos I've watched I actually believe him. (I realize it's dangerous to believe a politician...)
Many Jews get frightened by anti-Zionist rhetoric, and not for bad reason. People who hate Jews are generally anti-Zionist as well. Do Jewish leaders have a motive for accusing Corbyn of being anti-Semitic? Yes, some leaders are probably interested in protecting Israel from a party that might be sympathetic to enemies of the Jewish state -- the Palestinians.
So my answer is as vague as Corbyn's analogy. I don't feel strongly about what I think, but I think this is what happened:
- Corbyn took a shot at Netanyahu by comparing him and his ruling party to ISIS.
- Corbyn isn't racist or anti-Semitic himself, but deep-down he and other party members might sympathize with Palestinians.
- Some British rabbis are worried by Labour Party's anti-Zionist sentiment and have taken this opportunity to denounce Corbyn publicly.