Can anyone explain this frost phenomenon?
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.