wi - I'm no wise man that's for sure but I have had pain in that area myself for some time. It may be something completely different so please feel free to ignore anything I'm saying here.
There are parts of the calf muscles (peroneus?) whose tendons loop round the ankle and run under the outer part of the sole of your foot. I had alot of tightness in my outer calf and this was causing pain in the area you described as it pulled on the tendon. As you said, using a tennis ball eased the pain quite significantly.
So maybe running on the snow you changed your gait slightly and over worked part of the calf? If it doesn't come back running in normal conditions I'd just forget about it.
As I said, I'm no expert, just relaying what happened to me.
Hopefully for you it's just a one-off.
Oops - x-post with RR
PS. for info - high heels were absolutely not a contributing factor in my case. I've worn them for years and had no issues whatsoever 
Edited: 25/02/2013 at 21:23