Then she said quickly, and in a low voice so eager that it was unsteady: "George, you've struck just the treatment to adopt: you're doing the right thing!" She hurried out, scurrying after the others with a faint rustling of her black skirts, leaving George mystified but incurious.

He did not understand why she should bestow her approbation upon him in the matter, and cared so little whether she did or not that he spared himself even the trouble of being puzzled about it.
In truth, however, he was neither so comfortable nor so imperturbable as he appeared.

He felt some gratification: he had done a little to put the man in his place--that man whose influence upon his daughter was precisely the same thing as a contemptuous criticism of George Amberson Minafer, and of George Amberson Minafer's "ideals of life." Lucy's going away without a word was intended, he supposed, as a bit of punishment.
Well, he wasn't the sort of man that people were allowed to punish: he could demonstrate that to them--since they started it! It appeared to him as almost a kind of insolence, this abrupt departure--not even telephoning! Probably she wondered how he would take it; she even might have supposed he would show some betraying chagrin when he heard of it.
He had no idea that this was just what he had shown; and he was satisfied with his evening's performance.

Nevertheless, he was not comfortable in his mind; though he could not have explained his inward perturbations, for he was convinced, without any confirmation from his Aunt Fanny, that he had done "just the right thing.".