Stefano's in-joke
The is a scene where Norman's mother asks "what do you think about my new kimono?"
Norman replies "I think it's lurid"
In the Making of Psycho book, Stefano mentions a disagreement he had with Hitchcock in the script, and that Hitchcock wanted to remove the word lurid from one of the scenes because he didn't like that word.
Stefano must have threw it in Psycho 4 as an in-joke.