If fibreglass was used to insulate the attic in my house, what color, how does this insulation look like? Are fibreglass particles light enough to float like dust?

When the workers cut holes in the ceiling I noticed on the floor gray colored clumps of material that looked like dust cumps on the floor. Could this dust have been insulation material?

Most likely if just a little it is drywall dust or plaster

Sorry fiberglass looks like cotton candy and is pink or yellow

Sounds like you have " blown in shredded type " insulation, not all insulation is fiberglass. Usually blown-in is made from recycled cellulose material and looks like old newspaper wadded-up, wet and shredded so if you cut a whole in ceiling it will fall out, nothing to hold it in like backing on batted fiberglass insulation.. Lowe's sells shredded type and rents the machine to blow it in. Some attics you can't get a person in their, sounds like what happened in your case, guy had to cut through ceiling to get at whatever he was working on.