I see two perfectly reasonable possibilities that don't require a divine explanation:
1. Sheer coincidence. Also, it ain't exactly like shootings are an unheard-of event these days, sadly. They've been in people's minds a lot lately, so for someone to dream of one and there then be an actual shooting the next day really doesn't strike me as a very remarkable coincidence.
2. Or you never had such a dream, you're making it up.