scriptwriter's goof?
When White tells Evelyne about the swing, he says it was inspired by a painting of Watteau's.
The painting ('The Swing') is by Fragonard; there's no such picture by Watteau.
True, Watteau and Fragonard were both great inspirations for the arts of the 'gilded age'; but Frago's 'Swing' was in particular a famous picture.
I think it unlikely that White would have made such a goof; it likely came from the scriptwriter.
(Charles Bracket was an educated man...but of another age and milieu.)