"The frame contains". Meaning that every dead and then-living human was within the camera's view frustum, except for the three in the spacecraft. Not considering whether they're in the nighttime part of the planet or on the far side away from the camera; just that they're somewhere within the field of view.

Presumably many photos of the Earth from spacecraft have achieved the first part of that criterion, as Cassini's will. But the set of photos of most of the human race minus a few is much smaller: limited to the moon missions, because the shuttle and space station orbit too low to fit the entire Earth in one camera frame.

The photograph captured the light from the planet where everyone who has ever lived has spent their entire life, except for a small number of astronauts. More accurate, but less spiritual/sentimental sounding.