Twisted Treeline Fog....

So while playing some of the newly changed Twisted Treeline, I had an interesting effect appear. There was a thick layer of fog all over the map. When I asked the guys I was playing with they said they couldn't see it, even with identical video settings. The visuals were pretty awesome actually, really added to the spooky forest theme of the map, but that I was the only one that could see it struck me as odd.

So my questions: Is this a new randomly applying effect in Twisted Treeline, or a random bug.