I think it would be fair to reference the source, wouldn't you?

Were you told the story individually, or at an event?

Is the story well-known? Can you find multiple sources of it? Maybe if it's a broadly known story, retold many times and without a specific source, ie. (the imaginary, since I just made him up) Jim Bennings who was Howard's dorm mate and part time foodie journalist...then you could pretend you came up with it yourself.

Otherwise, and I don't see the downside in doing so, especially as Malcolm is a recognized author, reference the source.