Development board, not developer board. Also "development board" means "evaluation board" and has absolutely nothing in common with the term SBC, they are describing different things
It means it is a board for developing products before creating a custom PCB etc. it has nothing to do with it being a microcontroller board. A breakout board for a temperature sensor can count as a dev board, and any SBC counts as one too.  They are not terms for different things in the same category, they are completely unrelated terms describing different things entirely.
The idea of a board that can only do simple things and is bare metal programmed rather than with an OS, that is a microcontroller.