Willy Wonka's musical lock

Just before entering the production area of the candy factory in Willy Wonka And The Chocolate Factory, Willy Wonka plays a melody on a keyboard. He explains it is a ‘musical lock’. Mrs. Teevee says, ‘Rachmaninoff!’

Was that a Rachmaninoff melody?

According to IMDB, no:

Here’s the scene on youtube, along with brief fan commentary right afterwards.

The comments to this video suggest it’s an intentional error to help show the parents as idiots.

This is what I suspected, but I don’t know Rachmaninoff’s music so I wasn’t sure.

Seems less that she’s an idiot, but that she’s pretending to know more than she does.

Isn’t she also the one who says there are no such things as Oompa Loompas?