Might the first element reference be for specialized exporting?
Specialised Import Lists
If the first entry in an import list begins with !, : or / then the list is treated as a series of specifications which either add to or delete from the list of names to import. They are processed left to right. Specifications are in the form:
[!]name This name only
[!]:DEFAULT All names in @EXPORT
[!]:tag All names in $EXPORT_TAGS{tag} anonymous list
[!]/pattern/ All names in @EXPORT and @EXPORT_OK which match A leading ! indicates that matching names should be deleted from the list of names to import. If the first specification is a deletion it is
The fancy stuff (negation, tags, patterns) only work if the first item is such. Something like use Module qw( foo :tag ); will not work, since the code will skip expanding the fancy stuff if the first argument doesn't trigger it.
But that has nothing to do with the conjectured significance of the first item in @EXPORT_OK.