When the vehicle is traveling in a straight line, the differential travel gears are only spinning, not rotating. Is this argument right or wrong?

Right. When traveling in a straight line, the differential case and the planetary gears (the planetary gears do not rotate relative to the half-shaft gears) rotate together with the reduction gear passive gears . It's called a metric rotation.

Planetary gears to spare their own axis rotation is called rotation, the two wheels will be suspended, the direction of rotation is opposite, the same speed.

When turning, the planetary gears not only rotate, but also rotate together with the differential case, realizing unequal speeds on both sides.

When the car turns, the inner wheel travels a short distance, and the outer wheel travels a long distance, but the experience time is the same, so the inner wheel rotation speed w1 is smaller than the outer wheel rotation speed w2, there is a difference in rotation speed, and then the differential works, and the differential rotates at the rotation speed of w1 - w2.