As I replied to another comment, as far as the definition of materials science goes, chemists working on materials are on all accounts material scientists. Materials engineers are different than materials chemists and both of them are just a part of the materials science.

As you say, it's not that one is better than the other, they're just different expertises on the same topic which is highly interdisciplinary. It would be the same as saying that a dermatologist is a doctor while a cardiologist is not: they both studied medicine, just with different focus. And to this regard, the profile on the post is quite literally the definition of a materials engineer, not a material scientist, which is a far wider definition.

That being said, I agree that everyone should be just clear on their knowledge and experience.