Presumably they weren't computer GCSE papers, but edited so that topics not yet covered weren't included. Even in good years, very few subjects would have been nearly complete at this stage of the year.
Not sure why or how. DS did do lockdown home learning, but not excessively - approximately 2 hours a day. He's just had mocks in everything using actual GCSE past papers or equivalent and done really well. This is not showing off, I'm just confused as to how he can have missed so much teaching but still be where he should be.