@_ contains the arguments to the current (inner-most) subroutine, which is why the @_ in the inner subroutine is different from that of the outer subroutine. shift acts on @_ by default, which is why it gets the first argument to the inner-most function.

Strictly speaking,

    my @list = @_;
    print @_, ' out  return', "\n";
[download]

is the only content directly in sub formatlist, the rest is in an inner functio which has its own @_.