セラミックス is Ceramics. That's the official website saying that.
https://www.seikowatches.com/jp-ja/products/prospex/sbdx023
There is no doubt in translation here. In this case I'm believing the website over what an employee said.
https://www.seikowatches.com/us-en/products/prospex/special/lxlinecermet/
That's just about the LE's using cermet ^^