Evo said:
I will never forget a dream I had in the eighth grade. I was walking along the muddy school yard, trying to get to "the shacks", temporary trailers that were set up on the lawn to house additional classrooms.
In my dream, this kid I'd never seen runs up to me and starts stabbing me in the chest with a large knife. I must have had the same dream 4 times in one night.
The next morning, it had rained. I was holding my books in front of me and walked looking down to try to avoid stepping in large puddles, when suddenly, I walked straight into a guy. I looked up into his eyes and we both let out a startled gasp and turned and ran. He was the guy that had tried to stab me in my dreams all night, he apparently was just as afraid of me. I will never forget looking straight into the face of my murderer, although it was a dream murderer. I have no explanation for what happened.
Very eerie.
I hope you don't mind if I try my hand at some possible (non-parapsychological) avenues of explanation.
One possible explanation might be that the person you were predisposed to 'see' your dream murderer on this occasion. The dream sounds quite vivid and upsetting, so you may have been in some emotional distress on some conscious or unconscious levels the following morning. On top of that, the following morning you found yourself in the same context in which your dream occurred, which surely was picked up upon by conscious and unconscious cognitive appraisal mechanisms-- so you may have had some expectations of/alterness to danger in general (and perhaps more specifically, danger relating to the dream events) and an abnormally sensitive predisposition to react to startling or unexpected events in a fight/flight manner.
When you bumped into the person, given your likely cognitive and emotional state at the time, it's no surprise that you had a fearful, fleeing reaction. The unusual thing is that you remember this person looking just like your dream murderer. A number of factors could have been at play in determining this experience:
1. Brief encounter-- since you bumped into this person unawares while looking at the ground, and soon ran thereafter, you might not have gotten as sharp or complete of a look at him as you thought;
2. Priming effects-- the morning walk was similar to the traumatic dream, so you may have expected/been predisposed to completing the pattern on some level of processing, whether it was really warranted or not;
3. Memory effects-- memory is not a perfect, passive recording; it's constructive and malleable. In particular, memories pertaining to highly emotional/traumatic experiences are susceptible to poor/incomplete encoding during the experience and alterations/distortions upon subsequent retrieval. Given that this was at least a mildly traumatic kind of experience, the effects of (1) and (2) on the encoding and subsequent retrieval/reconstructions of the memory may have been magnified.
4. The dream image of your dream murderer also may have been retroactively subject to (2) and (3). Assuming you did get a good and accurate look at the person you bumped into, your memory of what the dream murderer looked like may have altered in some way to match what the actual person looked like.
You probably weren't aware of it.
And I hate dogs. 
I'm always worried I'm not actually dreaming and I'll drown.