Eu pensei que ele queria dizer que o Hagrid deveria parar de tentar mediar entre os Centauros e fazer com que ele fosse aceito e perdoado por eles.
A partir daqui podemos ver que Hagrid e Firenze se conheceram ao se encontrarem pelo menos uma vez antes do 5º livro ( na Floresta Proibida no 1º livro).
Firenze saved Harry Potter in the forest from Lord Voldemort, frightening him away and carrying Harry on his back to safety. Despite his heroics, his herd saw this as a dishonourable act, as they considered themselves too great to be ridden by humans.
About four years later, in March 1996, Albus Dumbledore, Headmaster of Hogwarts, hired him to teach Divination in Sybill Trelawney's stead, after she was sacked by Dolores Umbridge. But once again, the other centaurs saw this as servitude, and his colony attacked and banished him. They would have killed him were it not for the intervention of Rubeus Hagrid.
Bane: "Firenze! What are you doing? You have a human on your back! Have you no shame? Are you a common mule?" Firenze: "Do you realise who this is? This is the Potter boy. The quicker he leaves this forest, the better." Bane: "What have you been telling him? Remember, Firenze, we are sworn not to set ourselves against the heavens. Have we not read what is to come in the movements of the planets? […] Centaurs are concerned with what has been foretold! It is not our business to run around like donkeys after stray humans in our forest!" Firenze: "Do you not see that unicorn? Do you not understand why it was killed? Or have the planets not let you in on that secret? I set myself against what is lurking in this forest, Bane, yes, with humans alongside me if I must." — Bane scolds Firenze for letting Harry ride him
He was friendly with Hagrid, and seemed to get on quite well with Harry, who was on speaking terms with him unlike most students, who found him intimidating.
when the Centaur's herd turned on him for entering into "the servitude of a human" by accepting the position at Hogwarts as a favour to Headmaster Dumbledore, it was Hagrid who saved him.
Não é canon, mas minha lógica
Eu não acho que a menos que o livro diga absolutamente, que Firenze iria querer Grawp abandonado como ele foi abandonado por sua espécie. Lembre-se que ele tem compaixão, ele veio em auxílio de Harry e ele defendeu o que ele acreditava (mesmo que ele tivesse tentativas de vida). Firenze não aparece teria dito a Hagrid para matar seu irmão ou de volta feito, como ele mesmo não estava recuando.