We don't actually know if he lied. What we know is that he's not releasing the tape. Even if he did have it on tape, there's zero chance his lawyers would allow him to release it as it would show a pattern the president would have for recording all phone calls, even those to a bereaved soldiers family. Essentially opens them up to contempt of court and additional obstruction charges for failing to release all his other phone calls when he was asked for phone recordings between him and comey.