I think the fog was a different film and that’s why.

The ending was really good though.

Because the producers of the film couldn't afford rendering more that a couple meters away from the camera, they added the fog effect as a workaround. It worked so well that they re wrote the film around that.

But they could not call it "The Fog" as there already is a film named like that.

They used the same trick for the first few silent hill games.

From the moment the fog starts rolling in you just lose all faith in the movie and its' producers.

Ugh, don't give away the twist in the movie like that!

Fogs move too slow, but this is a Mist Hurry