That’s not in dispute, or would you disagree?

I don’t disagree.

It would seem to me that Israel and China should have a lot of common ground in dealing with islamistic terrorism, but geopolitics is preventing them from co-operating.

Kind of, but not really. The attacks in China were mostly spill over from the post War On Terror surge in Islamic extremism in the middle east, while Israel’s issues are tied into it’s conflict with Palestine that go back decades. The important difference is that Israel is trying to get rid of the Palestinians so it can take their land, and the Islamic terrorism has largely been in response to that. Meanwhile, Xinjiang has been a part of China for a long time, and the people living their are Chinese citizens, with the violence being a relatively recent occurrence.

That said, it would be a far better world if Israel was as restrained in it’s response to Terrorism as China, but that would require them to, at the very least, grant Palestinians full citizenship and voting rights.