Keep in mind they were talking about the "those scriptures which have been written by them of old" V12, so most likely they were talking about the Brass Plates, which doesn't burn and the fact that Zenos and Zenock was quoted to them and they were asked if they remember those verses, V3. it would indicate they were suppose to know who those Prophets were and what they said. it's possible someone, who was literate, read it to them on a regular basis, just like we do in our church services, people reading out loud various verses