<This case is interesting because it depends on the student's knowing at least two things: the meaning of failure in more 'canonical' contexts, and a bit of human psychology -- how people sometimes behave (linguistically) in the sort of situation presented. (But I'm repeating what you already know.)>
That's right. I've long had discussion of the same nature.
<The implication for teaching? Obviously, when "training the machine", one doesn't present only the negative examples and then expect accurate predictions when the machine is placed in test mode.*>
Some have suggested teaching pragmatic meaning in ESL classrooms. I think it could be a good idea to do so with younger people, i.e. those who have not yet a solid grasp on pragmatic use in their own language, but with adults, it may not be necessary. We could just point out that "trial", in the above (taking just one example) is being used ironically. Stll, I think all student should know that their are three possible ways to talk about meaning when discussing language. They should be taught the meaning of syntactic, semantic and pragmatic meaning - even if it is not using those words. Teachers should fine a way to communicate those ideas and stop using the word "meaning" as if it were clear to all.