The Amazing Power of Sedums...urmm, green roof plants in general

Cleaning out the old smart phone and stumbled across this picture. Last year I was up on a roof doing a little maintenance and stumbled across this. One story down and in the neighbors gutter are a couple of rather mature chives! At least a year old, I'd say. How'd they get down there? My guess is the wind came a blowing from the green roof and collected a few volunteers. They were gone months later after the long awaited gutter cleaning.