Classical mechanics is the Newtonian mechanics system.

Don’t take it out of context. Measuring displacement and time alone are certainly different. Rather, the measurement results of displacement and corresponding time are the same.

This sentence is relative to relative ethics. The classic saying in the theory of relativity is that the moving ruler becomes shorter.

So the meaning of this sentence in this question is that the physical quantities we measure in different reference systems do not change in any way due to the motion itself. That is, in different speed systems, 1m is 1m and will not become larger or smaller due to different movement speeds.

But in the theory of relativity, the greater the speed, the shorter the displacement. The longer it takes.