The linked project doesn't use any ObjC files at all. SDL2 has a bunch of Cocoa files[1] so you did use Cocoa even if unknowingly.
[1] https://github.com/libsdl-org/SDL/tree/main/src/video/cocoa
[1] https://github.com/libsdl-org/SDL/tree/main/src/video/cocoa
Considering CodaFi works for Apple now, he knows. Spoiler: he knew 11 years ago too.