Unexpected way to set up a Fusion Drive

[space-time]

I have a Mac Mini server 2012 with 2 hard drives. There was never any kind of Fusion drive on the machine. The first HD (lower bay) came with the OS (10.9.5), the upper HD is empty (will be my local backup). today I replaced the lower bad HD with a new SSD. I have a USB3 stick which has the 10.9.5 install on it. so the first time when I boot from that, I open Disk Utility just to make sure the new SSD is installed correctly and that the machine can see it. When I opened Disk Utility, I got this dialog windows.

first, there was never any Fusion Drive installed here. I am not quite sure why I got this message...

Second, I read that making a Fusion Drive involves messing up with Terminal, I don't think I saw an article that showed how to do a Fusion drive only with the graphical interface. This seems easier for those who do not want to use the Terminal.

Since I had no interest in a Fusion drive, I didn't continue, but I think this was cool.

[Onamuji]

Only happens when at least 1 drive in there was part of a core storage spanned volume.

Where'd you get the SSD?

[space-time]

The SSD was new (I partition and formatted in an external case first to check that it works). The other HD in the upper bay was factory installed and never had any data on it. So as far as I can tell, there was never any fusion in this Mac or on these drives.