Molly, you can't possibly know how much revision he has actually done.
He might have done tonnes, yet just wants people to assume he's intelligent enough to get by without much revision.
Or, he may have lied about the amount of revision he did for his GCSEs and done quite well off his own back.
As Prudie very well stated, everyone is different. Some people do amazingly well with no revision. Example; my husband did really well in his education, and he would quickly skim through his books about an hour before his exams. Simply because this was the optimum way his brain absorbed information, and he would have it fresh and ready for the exams.