>Wrong. https://en.wikipedia.org/wiki/Cohesion_(computer_science)
>
>A thing must be internally cohesive. It must have loose connections to other things. Even if all of those things make for a single thing, it still has nothing to do with where the blueprints are stored at design time.


Wrong...

from the same link.
Related methods are in the same source file or otherwise grouped together; for example, in separate files but in the same sub-directory/folder.

This is for the obvious reason that you don't have to make changes in multiple source files an it then is obvious that methods/functions belong together. By putting functions into separate files you lost the cohesion of the source code altogether, because it is not obvious which functions belong to what module.