In this day and age, nothing surprises me.
The question also hinges on the nationality and age of the questioner.
A common 5.25" floppy is about 13 cm in size. Perhaps the young teacher
didn't have his units correct.
People often don't believe me when I tell them that the floppy disc
actually hails back to the 1950s. But it does and was not used for
digital recording.
--Chuck