It's pretty dang easy to misjudge distances and closing rates in a plane or helicopter, especially at night.
The only thing you have visually is direction / angular velocity.
If the airliners was approaching faster than the helicopter it could have been approaching from behind. How large is the field of view of a UH-60?
Massive, you're practically against the glass. Visibility below is more obstructed than visibility above or to the sides.
(Also at a low altitude in a large city ... lots of lights.)