Join Date: May 2013
Location: N. Vancouver, BC
Car Year: 2014
Car Model: 2.0 XT
I suspect it's just some condensation. The freezing makes it really stand out.
No harm cleaning it up though. Wet interiors encourage mould and that sucks.
Once everything melts, soak it up with a towel (don't store the wet towel in the car!). Get the floor mats and carpets dry as you can as well. Then, if the weather is warm enough, you can give the sunroof the "hose test" to look for leaks. Basically, give it a good (low pressure) soaking, and see if any water can get through.
I had some pretty serious condensation on my WRX sunroof this year. The inside of the glass was dripping with water. After cleaning everything up, all I did is crack the sunshade open a bit after parking the car (usually I close it). That allows for some airflow around the glass, and it seemed to help. The sunroof itself was not leaking.