I have a couple of neighbours who are buggers for doing that.
I can remember once when dd2 was very small, i had been ill and had caught up the washing, i'm talking 3 full lines and a square rotary drying filled to capacity and he decided to start doing block paving on his patio, all the washing had to be washed two or three times to get the dust out again, i was very very very especially as we didn't even get an apology.
Saying that, this is from people who either
a) NEVER hang washing out all during the dry days
b) Leave washing out for days on end, i think the longest they have left stuff there is 8 days.
Just be thankful (or hopeful) its animal poo. One of our local farmers uses recycled human stuff that he allegedly gets from the waterworks. He has a tendency to do it when the wind is blowing away from his house, and towards town, so everywhere honks until the stuff settles.