Does this mean my fusion drive has split?
Note that the article says "in the Finder". Disk Utility shows you more detailed information, because it's ... well... Disk Utility. The Fusion logical volume is stored within a "container" data structure. You may see more information if you have checked "Show All Devices" in the View menu.

A fusion drive is usually made of 1Tb mechanical drive with a 120Gb SSD. If your Fusion drive had "split", you would see two separate volumes on the Desktop.
(Oh, and you wouldn't have a working system, as both volumes would be unreadable and all your data would be lost!)