Both Uses of

discreet
in
The Fountainhead

People were gaping at Wynand—discreetly and with practiced camouflage, but gaping nevertheless—and their attention included the two guests at Wynand's table.†
Chpt 3.3 *

discreetly = in a manner that is unlikely to attract attention or cause embarrassment

Definitions:

(1) (discreet as in: discreet--not showy or gossipy)
trustworthy with secrets or subtle (not attracting attention)

This sense of discreet sometimes indicates that something is small (so as not to attract attention) as in "discreet earrings."
(2) (discreet as in: discreet--not foolish)
sensible and careful; possibly having good manners

This sense of discreet is more commonly seen in classic literature than in modern writing. There is may also refer to having the judgment to exercise good manners.