Ah ok - the reason for the confusion on this point is due to this documentation page.
Where it says:
- A package directory is a directory containing the source trees of a set of packages as subdirectories, and forms an implicit environment. If
X
is a subdirectory of a package directory andX/src/X.jl
exists, then the packageX
is available in the package directory environment andX/src/X.jl
is the source file by which it is loaded.