I think most people don't realise what "no revision" means; many people claim this, but they do little revision (a week or day before the exam) and attend classes.
I actually did no revision at all, not even 5 minutes before the exams, didn't do a single piece of homework and attended 70% of classes, So I missed 3 days per 2 weeks on average, which is a lot for a GCSE student.
I find it difficult to believe that someone who has done no revision at all gets all A*s, even if you did 20 mins of revision that doesn't count as no revision.
My results were similar, but a few more Bs and Cs, but that's because GCSEs don't really test much in terms of intelligence, having done no revision, I didn't deserve Bs and Cs, I should have failed most of them, but even me not being academically inclined and attending 70% of lessons was enough for a B, that's not how it should be.
Same goes for A level, even though it's more difficult than GCSE and revision is required, it's not insanely challenging. However having to recap GCSE material when starting AS maths was a pain. Which goes to show how easy gcse maths is because I got an A (my only one) and most people were saying that C1 (the starting module of a level at the time) was basically mostly GCSE and I didn't recall ever learning most of the things.