"In the same way, monks, those things that I have known with direct knowledge but have not taught are far more numerous [than what I have taught]. SN 56.31
I think the Buddha had to explain things according to the accepted knowledge of the times, even if he knew that the accepted knowledge was incorrect. Why? Because otherwise, he would end up wasting time and energy trying to refute the accepted knowledge, time and energy that would be best used to propagate his message.