It would be good for you to notice that a lot of people regarded that story as academically trustworthy. Teachers are responsible for what they share with people no matter where the lessons originate from. Me, as well!
If I open Sibelius or go to Noteflight online, I can choose 30 key signatures for a given piece of music.
Two with no sharps or flats.
7 major sharp keys.
7 major flat keys.
7 minor sharp keys.
7 minor flat keys.
Should bass players not use notation software? Rather, if a bass player is a musician who has a piece of music shared with him in one of these keys be ignorant of them?
I think this is the best explanation of it that I've seen so far:
Keys in Music | Harmony | StudyBass
For those who don't want to click the link, Andrew Pouska says because there are 12 major scales, there are 12 major keys. Likewise, there are 12 minor scales and, therefore, 12 minor keys. So there are 24 keys all together.
Three of the major keys can be named 2 different ways – one way with sharp note names, and the other way with flat note names. This results in 15 different major key spellings.
As an example, the keys of Gb major and F# major contain the exact same notes. The former is spelled using flat note names (Gb, Ab, Bb, Cb, Db, Eb, and F), while the latter is spelled with equivalent sharp note names (F#, G#, A#, B, C#, D#, and E#). There will be times when choosing one spelling over another is preferable. (More on that later.)
In the same way, there are 15 different minor key spellings.
In total, there are 24 keys and 30 ways to spell them. In the next few lessons covering the circle of 5ths, I will show you how you can start memorizing all 30 key spellings. It sounds far scarier than it is, but it will take some effort.