Why does Winnie get reminded about her grandfather's funeral when talking to the stranger?

But Winnie, though she was half charmed, was suddenly reminded of the stiff black ribbons they had hung on the door of the cottage for her grandfather's funeral.

Winnie meets the man in the yellow suit in chapter 4.  The man is perfectly cordial and friendly to Winnie.  In fact, he is even a bit charming, and those are Winnie's initial feelings about the man; however, Winnie does not fully trust the man.  She feels...

But Winnie, though she was half charmed, was suddenly reminded of the stiff black ribbons they had hung on the door of the cottage for her grandfather's funeral.

Winnie meets the man in the yellow suit in chapter 4.  The man is perfectly cordial and friendly to Winnie.  In fact, he is even a bit charming, and those are Winnie's initial feelings about the man; however, Winnie does not fully trust the man.  She feels as if something is "off" about the guy.  The black ribbons and the funeral thoughts help the reader and Winnie better understand that the man in the yellow suit isn't what he seems.  The black ribbons at a funeral might look nice and neat, but they represent a terribly sad situation.  A loved one has died.  Like the ribbons, the man in the yellow suit might appear and sound nice and neat, but he most definitely represents a dark, evil force in the novel.  Winnie being reminded of her grandfather's funeral is her internal warning system going off about the stranger.