DS's school predict grade 9s. If you've done an external national exam, or more than one, and you've come near enough to the top each time that you were 1/200 or 1/500 or 1/1000 etc, then you can see how the teachers might feel confident to predict 1/40. (And on the same theme you might also find an exam easy that was designed for most of the population if you genuinely have taken and passed much harder exams).
But otherwise, I'd generally agree that the 9s really must just be aspirational targets, even when the teachers use the word "expected grade" instead. And, yes, without a doubt, high grade predictions are a source of stress in a conscientious teenager.