Sounds like there was quite a few out flying yesterday. Not surprised, calm winds and sunny. I didn't fly near any residential homes, and always try to be respectful when flying. Keeping my flights all very short, generally under 3 minutes and plan my flight paths ahead of time so as to cause as little disturbance as possible. I know how offensive drones can be to some people, so I always keep that in mind. I also avoid taking photos with people in them, only buildings and landscapes.
Given that complaint was in a residential area, flying at just 100ft. It was probably taking images for a real estate listing.