An ND filter alone is very unlikely to create that look. Based on the described image characteristics, it was probably heavily altered in post-processing.

Why: an ND filter mainly reduces light so you can use a longer shutter speed or wider aperture. If the shutter were long enough to create strong motion blur, moving water would usually also blur into a smoother, “glassed” look. If the water still looks relatively crisp, the exposure was probably not long enough for an ND-based effect to explain the whole image.

The deep blue “night” mood and the unusual yellow on the road are stronger clues for color grading or compositing than for a physical filter effect. The road markings/color also sound too uniform or stylized to be a natural result of filtration alone.

You can get somewhat closer in-camera with careful white balance, shooting in low light, and possibly a long exposure under the right conditions, but matching that exact effect would typically require post-processing.