I agree that's 100% what happened in this specific case. The customer had absolutely no reason to suspect the information they were given was bad, and the airline should have honoured the deal.
A top-level comment on the post was also mine, by the way, in which I expressed the same and said "Shame on Air Canada for even fighting it."
Air Canada were completely and utterly wrong in this case - but I haven't been talking about this case! At least, I wasn't intending to!
If it seemed that way I can understand now why people were so vehemently against me.
My comments in this chain have all actually been trying to discuss how to determine, in the general case, which party is "in the right" when things like this happen.
There are cases like this Air Canada one where the customer is obviously right. We can also imagine hypothetical cases where I personally believe the customer would be in the wrong - for example if the customer intentionally exploited a flaw in the system to game a $1 flight - which is again obviously not what happened here, it's just an example for the sake of argument.
My fundamental point at the start of this comment chain was that I don't actually think we need any new mechanisms to work this out, because the existing mechanisms we already have in place to determine who is right between a company and a customer all still apply and work exactly the same regardless of whether it is AI or not AI.
And that mechanism is, fundamentally, that the customer should generally be considered right as long as they have acted in good faith.
That's why I'm very pleased with the ruling that Air Canada were wrong here and they cannot dodge their responsibilities by blaming the AI.
I'm honestly glad I can put the stress of this days-long comment chain behind me, since it seems we weren't even arguing about the same thing this whole time!