The term "disc" for storage predates optical media. "Disc" was the common spelling for a disk (like a floppy disk) on British 8-bit computers like Amstrad CPC or Sinclair Spectrum.[1][2]

It seems like the distinction simply comes from British and American preferences.[3]

I have no idea how Apple jumped to such an arbitrary conclusion.

[1] Kempston Disc Interface manual: https://k1.spdns.de/Vintage/Sinclair/82/Peripherals/Disc%20I...

[2] Amstrad Disc Drive Interface manual: https://www.cpcwiki.eu/imgs/3/3f/DDI-1_User_Manual.pdf

[3] Etymonline entry for "disk": https://www.etymonline.com/word/disk

Disk was already the standard spelling in the UK by 1984 (in a computing context), just as program was used in preference to programme. But Amstrad mistyped it as disc on the plastic mouldings for their first CPC, and were too cheap to change them. Consequently CPC 3in disks were always called discs even into the 90s.