I think the article is saying that the predicted magnitude of the comet is -16.
What could possibly make the comet, which is very, very small compared to the moon, be that bright? I think the journalist have misunderstood the calculation or maybe read ~16 (approximately, which has been the current magnitude) as -16.
From nasa.gov: "In the best case, the comet is big, bright, and skirts the sun next November. It would be extremely bright -- negative magnitudes maybe -- and naked-eye visible for observers in the Northern Hemisphere for at least a couple of months."
If NASA says it _might_ reach negative magnitudes, I'm pretty sure the -16 is wrong.
What could possibly make the comet, which is very, very small compared to the moon, be that bright?
The tail, which is very, very big compared to the moon.