I recommend that you get a cloth and wipe it off, then go outside and touch some grass. If this is the only thing you can find to whine about call it a win.
Oh yeah call the cops on the toddler who stepped on your lawn for trespassing too, and don't forget to press charges. FFS this is aggregate powder it's completely harmless it just gets everywhere.
And the contractor will laugh in your face. If you tried to withhold payment over some bullshit like this, the contractor could take you to small claims and definitely win. Or put a lean on your property. I really hope your comment was supposed to be sarcastic.
As long as you don’t lick it or sprinkle it in your eyeball you’ll be fine.