This is what happens when you get some nice sunny weather after a week of rainy humid weather.
If you try to dry your clothes on a rainy day they take too long to dry, and could end up smelling a bit funky. So on a nice day, out they come. It's worth bringing up that almost nobody in China has a clothes dryer. Dryers are high energy users, and they are an expensive purchase besides. In America, almost everyone has one, or uses one at a laundromat. I've found that life without a dryer is ...completely normal and unremarkable. The American view of the dryer is that it is a need and not a want; the majority of people in modern society don't question this assumption. But actually I've come to think it's an unnecessary want.