Specks/Blotches on basement ceiling wood joists

This seems to be around the edges of the basement and looks like someone literally took spray paint. I can provide more pictures if needed. Any ideas as to what this is?

Drywall finish and/or paint overspray.

Hmm, I don’t know if it’s drywall finish. It’s just the main floor shown there and then the drop ceiling, there’s no drywall. What would the paint overspray be for?

Was the ceiling grid ever painted…they would spray that. Looks like paint to me.

What happens is paint contractor tapes off ceiling and uses a high pressure paint sprayer and sprays the wall. The paint overspray finds small gaps between edge of drop ceiling and wall. That is why it is only along the edges. This is very common we see it often.

Often painters will take all the doors of the house to one location and tack them together with 1x and spray them. Looks like overspray from that or a similar process.