The "implicit argument" is the perl function 'caller' which reports the name of the package making the call, among other things. Each individual package that exports things has to deliberately look at 'caller' and decide to write functions into the package one level up. They are also free to do completely different things.

For this example, as tobyink and hv already pointed out, strict and warnings are special because they just modify the state of the interpreter during the compilation phase (which affects the rest of the compilation of the calling package) rather than actually exporting anything into the caller's package.