Probably because you studied in the UK? I don't know why the requirements are not uniformly enforced, I'm just highlighting what has recently changed, especially with India. For South Africa, we don't have SDS stream, but our country's list mandates english test and PCC. Not all countries require PCC and it's not on IRCC official checklist.I referred to the study permit guide for my Visa office; from what I remember, an English-language test was recommended. In any case, I did not submit any proof of English language proficiency and my application was approved