I believe what's going on there is that the water is uneven, so it is more scattering the light when it reflects it than properly mirroring it. Each part of the street is reflecting light from all sorts of directions to all other sorts of directions. You only see the headlights though because the headlights are by far the brightest source of light hitting the street. As a result, the headlights are reflected to your eyes from a much greater area of the street than they would if the street was a perfect mirror.