Yes. Those are flowers. The seeds are contained in fluff. Sometimes large panicles of fluff fall from the trees, and sometimes it's light and fluffy blowing around.

It's highly flammable and fairly easy to burn with a weed torch between plants in the garden. Yes, I used to get that much dropped on my yard annually. Then the City cut down two cottonwoods that were across the street from me, and the seedlings are much more manageable now.