Three boys entered, and Harry recognized the middle one at once: it was the pale boy from Madam Malkin's robe shop. He was looking at Harry with a lot more interest than he'd shown back in Diagon Alley.
"Is it true?" he said. "They're saying all down the train that Harry Potter's in this compartment. So it's you, is it?"
(Harry Potter and the Sorcerer's Stone)
Is ‘all’ a pronoun and indicating ‘they’? If yes, why does it separated from they and be placed in the middle of the sentence?