The particles were the Scratch Resistant Coating flaking off. It was probably a cheap film that had little or no UV protection. The UV inhibitors are not reflective coatings as stated in the article but a coating on the first layer of polyester that converts UV into a faster wavelength which is then reflected or absorbed by subsequent layers of film or by the glass itself. UV inhibitors were put into the construction process of window film since the early seventies. They were put in to protect the film's metalized and dyed layers from UV. UV attacks the film and causes dyes to fade and metals to decompose (lose ions). That last layer of your film is the hard coat. When exposed to UV it breaks up. Another reason window film is not installed on the exterior!
If you need to remove it, sweat it. That's the best way. Cut black garbage bags to the size and shape of your windows. Spray the film surface with soapy water and put the plastic on the film side of the window. The soapy water will hold the plastic to the glass. Let it sit in the sun for an hour. The film should peel. If it leaves glue, you can scrape it with a new clean 1" razor. Try Goo-Gone or Goof Off. If there is glue on the defroster clean it with 0000 steel wool and solvent.