The friend who changes the subject at the right moment may be offering protection nobody needs to announce.

Some kindness only works while it goes unmentioned. A conversation is heading somewhere that would expose someone, a friend turns it lightly aside, and the room moves on without ever registering that anything happened. Announcing it afterward would undo the exact thing it achieved, which is why the good version stays quiet.

Watch for the moment a subject should turn, and turn it before anyone has to ask. When it is done for you, let it pass without thanks, and remember who did it.