Well, both are true in different ways. The dust would get trapped in the wool rug as it drifted down out of the air, but then when you walk on or vacuum the rug, a bit of dust will be stirred up. In a perfect world, you’d have bare wood floors that you vacuumed daily with a HEPA filtered vacuum. You could have cotton throw rugs if you washed them in a sanitary cycle twice a week. A good compromise is the good wool area rugs that you vacuum weekly.