I've always thought as there being multiple stages to petrification, or at least different kinds.
Its sort of like how most people who hear "Schizophrenia" automatically associate it with seeing things that don't exist, when in reality that's only the most severe cases.
Petrification I imagine is just a scale of how paralyzed you become. A gorgon could easily turn you to full stone, but may not always need someone to be stone in the first place. This is magic, so it could be mysterious how maybe despite looking stone, the person is alive underneath, or maybe in the most severe case, it kills them. Maybe they just become paralyzed from the neck down, or maybe totally paralyzed on the surface, but some fragment of the magic keeps them alive in a condition where they should be dead - which is a lot of what petrification is already.