This is where it gets tricky, typically, cmu means "clay masonry unit" however it can also be used for concrete masonry unit, in which case he is using cheaper concrete "bricks" instead of fired clay units which hold color and are considerably more durable and appealing. I would make sure he's very clear on what kind of masonry units he will be using, although, it's likely you've already picked them out in which case, you will know whether you've chosen clay or cheaper concrete bricks.

CMU = Carnegie Mellon University, in Pittsburgh PA.

Thanks berlin. (cute garyg) For the inside of the place where the wood burns, he did use the yellow fire-brick. The framing is cinderblock atop a poured concrete base.

Thx!