Did your dream experience happen early in the morning? Most people sleep at night, and wake up around 7:00am, 8:00am, 9:00am, ect. Our most vivid dreams and lucid dreams happen in REM state (rapid eye movement), it's the deepest sleep our bodies get. Our physical body is paralysed during REM sleep so we don't physically act out our dreams. REM sleep leaves our astral body seeing through our closed eyelides or floating in the air.
I assume you might have met your grandfather in the Astral world. However, during my astral projections, everything looks starry. The word astral means star. So the astral plane, or at least higher astral planes, has starry energy.
If your grandfather is 'crossed over' to the astral world/other side, than I doubt you can keep away from him. We can see each other on the astral plane, just as we see each other here on the physical plane.
Good luck.