"Call me Hagrid," he said, "everyone does. An' like I told yeh, I'm Keeper of Keys at Hogwarts -- yeh'll know all about Hogwarts, o' course.
"Er -- no," said Harry.
Hagrid looked shocked.
"Sorry," Harry said quickly.
"Sorr?" barked Hagrid, turning to stare at the Dursleys, who shrank back into the shadows. "It's them as should be sorry! I knew yeh weren't gettin' yer letters but I never thought yeh wouldn't even know abou' Hogwarts, fer cryin' out loud! Did yeh never wonder where yet parents learned it all?"
"All what?" asked Harry.
"ALL WHAT?" Hagrid thundered. "Now wait jus' one second!"
He had leapt to his feet. In his anger he seemed to fill the whole hut. The Dursleys were cowering against the wall.
"Do you mean ter tell me," he growled at the Dursleys, "that this boy - this boy! -- knows nothin' abou' -- about ANYTHING?"
(Harry Potter and the Sorcerer's Stone)
What does the phrase mean? (I don’t find any relationship between angering and he filling the hut.)