Olhando para a cotação em questão, é importante notar a próxima parte.
Harry heard the grinding of benches and then the sound of the Slytherins trooping out on the other side of the Hall.
‘Ravenclaws, follow on!’ cried Professor McGonagall.
Os sonserinos não foram forçados a sair, eles apenas escolheram ir embora. Nós vemos isso nesta frase:
The Slytherin table was completely deserted, but a number of older Ravenclaws remained seated while their fellows filed out: even more Hufflepuffs stayed behind, and half of Gryffindor remained in their seats
A observação de que a mesa da Sonserina estava completamente deserta é inútil se McGonagall os expulsar; é, no entanto, digno de nota se nenhum deles permaneceu, em comparação com o resto das casas.
Atualização, esta citação mostra claramente a intenção da McGonagall de oferecer a todos a chance de ficar
‘The time has come for Slytherin House to decide upon its loyalties,’ interrupted Professor McGonagall. ‘Go and wake your students, Horace.
Ernie Macmillan stood up at the Hufflepuff table and shouted, ‘And what if we want to stay and fight?’ There was a smattering of applause. ‘If you are of age, you may stay,’ said Professor McGonagall.
E sua breve observação na citação em questão deve-se ao comentário de Pasny Parkinsons aqui,
Then a figure rose from the Slytherin table and he recognised Pansy Parkinson as she raised a shaking arm and screamed, ‘But he’s there! Potter’s there! Someone grab him!’
Before Harry could speak, there was a massive movement. The Gryffindors in front of him had risen and stood facing, not Harry, but the Slytherins. Then the Hufflepuffs stood, and, almost at the same moment, the Ravenclaws, all of them with their backs to Harry, all of them looking towards Pansy instead, and Harry, awe- struck and overwhelmed, saw wands emerging everywhere, pulled from beneath cloaks and from under sleeves.
É muito claro que McGonagall deu aos Sonserinos a chance de se juntar à luta, e eles escolheram como um todo para sair.