Cowardy Custard is a musical revue and was one of the last Noël Coward shows staged during his life. It was devised by Gerard Frow, Alan Strachan and Wendy Toye. A book, also titled "Cowardy Custard", was published in connection with the revue, similarly celebrating the Coward image.
Cowardy Custard was also a movie to continue celebrating the Coward image.
It's not either correct or incorrect because there's nothing to prove or disprove that a movie wasn't made given the context.  I believe the system got it wrong because there was nothing implying that a movie had been made.