Education isn't dependent on literacy. Aristotle famously decried that (paraphrasing) "kids these days don't know anything anymore because they just write it down and don't actually memorize it"

Robert Jordan's Wheel of Time is a work of fantasy written in the last 50 years, not an accurate account of historical humanity.

In real life, bards were specifically Celtic minstrels who maintained an oral history for the pre-Christian Celtic people, who notably didn't write down their history. They used meter, rhyme, and song structure to help them commit the words to memory.