Did Luke write his Gospel and Acts from his own memory?
No. Although Luke remembered events and kept much in mind, he did not write Scripture from his own memory. Paul writes that all Scripture is given by inspiration of God, so Luke's Gospel and Acts were divinely inspired rather than merely recalled.
Les explains that some give Luke credit for being a tremendous diarist who kept a perfect daily diary, especially as he traveled. But he rejects that idea. He says many things were in Luke's mind, and he remembered events that took place, yet he did not write the Scripture from what was in his memory. This fits Paul's statement in 2 Timothy 3:16 that all Scripture is given by inspiration of God.