Is this black material in my HVAC air duct mold?

I live in an apartment complex in the southeastern United States. The apartment complex is made of brick so is probably fairly old, but my apartment was renovated just before I moved in. It has central electric AC and heat with the combination AC/heat unit inside a vented closet in a wall.

I recently began to notice small black pieces of crumbly material on the floor and furniture underneath the ceiling air ducts. Today, I removed the register from one of the ceiling vents and noticed that the ductwork inside is very dirty. Some observations:

1. Most of the inside is covered in white material. I wonder if they left this vent uncovered whenever they were preparing/painting the ceilings.
2. Some of these white dots appear to have become black.
3. There is a gap between the metal vent and the ceiling, and there is more black material in this gap. This material has a fuzzy-looking surface.

The pieces I found on my floor/furniture look similar to the black pieces in (2) and (3) so I feel confident this is the source. So my question is this: is any of this material likely mold? My first thought is that it could be insulation from the attic space, but I couldn’t imagine why it would be this color. Thanks for your help.