The difference is between acceleration and g-force. Falling towards earth in a vacuum (or orbiting earth in a vacuum) you are experiencing 1g of acceleration but zero-g of g-force because you and your spaceship are accelerating together and you aren't meeting any mechanical resistance to the acceleration.
Once you start hitting atmo the velocity you've built up from your 1g of freefall meeting the resistance of the atmosphere creates g-forces.
Once you start hitting atmo the velocity you've built up from your 1g of freefall meeting the resistance of the atmosphere creates g-forces.