The post title is wrong and was poorly transcribed from the article. The product is named M-DISC.

It is a convention that optical discs are discs, and floppy disks or hard disks are disks. It is not a hard-and-fast spelling rule, but since there is indeed a set of official standards for Compact Disc and Digital Versatile* Disc, you can be sure that any conforming optical disc won't be spelled with a "k".

* Were you surprised that the "V" doesn't stand for "Video"?