More often than not, we see people using the two terms "scratch-proof" and "scratch resistant" as though they are the same. This might not be unconnected to the fact that both terms are used for materials that can resist external factors. Scratch-proof refers to the quality of a material, which makes it resistant to being scratched.
Scratch-proof materials are materials that cannot get scratched, not minding how often they are exposed to various external factors. On the other hand, scratch-resistant does not hold the exact meaning as scratch-proof when referring to materials that cannot get scratched. Scratch-resistant materials can also resist external factors, but their degree of resistance can't be compared with that of scratch-proof materials.
What this means is that they are less likely to get scratched by external factors. I believe most materials that are referred to as scratch-proof are nothing but scratch-resistant materials since they usually end up getting scratched, although it may take a very long time for this to happen.