Why does Sissy Jupe’s response to her father’s absence surprise and astound Mr. Gradgrind?

Sissy's response was one of terror, and her announcement that she was going to search for her father at the Booth and would be back in a minute, once again appalled Gradagrind with its misrepresentation of fact. 

‘Father must have gone down to the Booth, sir.  I don’t know why he should go there, but he must be there; I’ll bring him in a minute!’  She was gone directly, without her bonnet; with her long, dark, childish hair streaming behind her.

‘What does she mean!’ said Mr. Gradgrind.  ‘Back in a minute?  It’s more than a mile off.’