I think the questions they asked him were badly chosen to get useful answers and that he probably answered truthfully.
Question: Did you ever use
whole recordings of works by other artists?
Answer: No.
Meaning: He mixed several artists' works together or something similar.
Question: Did you ever produce a recording that had
none of Joyce's playing in it?
Answer: No.
Meaning: They all had at least a few notes of her playing in them.