The self-possessed young woman who stood before him looked no more out of place and impossible in Mrs.
Wyeth's dignified and aristocratic parlor than she had in the store where he had last seen her.

Her gown was simple and inexpensive but it was stylish and becoming.

And her manner--well, her manner was distinctly more at ease than his at that moment.

Mary had been but eight weeks among the Misses Cabot's young ladies, but she had used her eyes and her brain during that time; she was adaptable and had learned other things than those in the curriculum.

Also, she was prepared for this meeting and had made up her mind to show no embarrassment.
So the usually blase Samuel was the embarrassed party.