When Aeana beat the game, she looked at the credits for the people who made it. It was mostly Matrix staff.
Main programmer: Masaru Imaoka (Matrix)
Other programmers: Tomohiro Ishikuro, Takao Fukaya (Matrix)
Art director: Shintaro Majima (ArtePiazza)
Planning director: Masayoshi Saito (not sure)
Technical director: Hideyuki Kato (Square)
And correct, Matrix didn't do DQIV PSX, but they did code the DS game.