However, Wittgenstein is not criticizing Malcolm just for supposedly having wrong factual beliefs, but for mere willingness to use probabilities about beliefs and behavior of people that are conditional on their natonality. He is objecting to the very idea that the probability of the British government commiting a certain act may be different from the probability of some other government committing it, or that certain broader norms that also prohibit such behavior might be a matter of exceptionally strong consensus among the British, which would by itself provide strong evidence that their government is unlikely to exhibit it.
I think we are interpreting Malcolm's position very differently. Malcolm isn't saying "I would be surprised; I put a low probability that the British government would do that." Malcolm appears offended- it is impossible because the British are too decent. You are right that one could, say, be less surprised by an American assassination attempt than a Canadian assassination attempt based on past actions of the governments, but that's not what Malcolm is doing here. He's exhibiting a nationalistic, self-serving bias, which Wittgenstein is right to object to.
Here's the new thread for posting quotes, with the usual rules: