Well, to be fair the proposition that the assassination attempt had British backing implicitly means that it had systematic approval in at least some government division, so it's a rather stronger claim than saying that at least one British person was willing to commit resources to backing the attack. But it did seem to me that Wittgenstein was criticizing his student for naive and sloppy thinking (which he was indeed guilty of) not for having the belief that there can be prevailing trends in national character.