Seems to me the main difference is that all the particles in the gyro are trying to go in a straight line, but can't due to being a part of a rigid structure. Y

Seems to me the main difference is that all the particles in the gyro are trying to go in a straight line, but can't due to being a part of a rigid structure. You should be able to tell the difference by dropping a ball bearing. It will land "straight down" if it's gravity, but move "to the side" if it's rotating.