pride in beauty

She had a sylph-like form, not thin but full-bodied within the
limits of her graceful frame, well rounded on the hips, with an
arched narrow waist from which descended the folds of her
trousers and above which were her full, round, globular breasts,
jerking slightly, for lack of a bodice, under her transparent
muslin shirt. Bakha observed her as she walked along swaying.
She was beautiful. He was proud of her with a pride not
altogether that of a brother for a sister. (15)


What is Bakha’s pride for his sister if it is not altogether brotherly?