Look at this amazing frost I woke up to in Sooke, BC, Canada. This was so very cool to wake up to.
I am going to take a guess and say these are Frost crystals. There are few conditions that need to be present in order for these to develop
1) Light wind
2) Relatively high humidity(some water vapor source perhaps nearby)
3) Depending on your elevation - was this somewhere near a mountain basin ?
As opposed to snow crystals frost crystals form more near the surface
You can read this article Frost crystal and if the answers are in the affirmative then you know these are the conditions that caused these crystals to form.