Agree with you! My first thought would be the same, until I get more information that proves otherwise, such as getting closer, looking at the person sufficiently close, perhaps briefly talking to them, have they traveled this route before, crime in the area, weather conditions, commonly traveled by other ppl to get to the store, etc.
There’s another clue I always look for when I’m walking down the street in NYC - is the guy in the hoodie walking quickly with purpose in his step - or is he walking slowly, looking at people, and generally seeming not to have a destination? That’s another thing I’m wondering about in this Zimmerman mess.