I saw this out the kitchen window a few minutes ago and ran out into the backyard in a panic. The house was on fire! Except that it was coming from the dryer vent. So the dryer was on fire! Until I stepped into the cloud of "smoke" and it smelled sweet and clean, like detergent, and not burnt at all.
Yes, that is a cloud of dryer steam. Apparently living in a constantly warm, dry climate for a year or so is enough to remove the memory of what dryer steam looks like coming out of a vent.