None of the magneto-optical discs/mini-discs in square cases were anything but round, were they?
Holographic/“3D”/“5D” discs have not been marketed yet, to my knowledge.
The people who asked about CDs may never have seen those, but if they had they wouldn’t necessarily had a clue that the media in the square was circular.
This reminds me of a demo I did in Computer Literacy classes back in the day. Students kept calling 3.5" floppies “hard drives” since the case was harder than 5.25" drivers. So I’d take 3.5" floppy and rip it up and flap the disk around to show that it really was floppy. They were amazed at a prof doing something so destructive. (Failed floppy disks were all over the place. No loss.)
I also in one era used some CD devices that had the square holders. You did not want to lose those.
Ah, caddy-loading CD drives.
If you have very few CD ROMs and just a couple of caddy-loading drives, it was a convenient system of storing and quickly loading or swapping media. But buying caddies added up quickly if you had more than a few.
Back in the early days, CD recorders came only in caddy-loading versions. (They also were skuzzy-only.)
Actually, I have a caddy-loading CD-ROM drive with a proprietary Sony interface. Pretty weird.
I might use the thing if it actually were SCSI, since I still have several vintage PCs with SCSI busses.