Interesting question
I don't have a direct answer, but do have some ideas...

File::Touch uses the following sub to do the work:

    if (-e $file){
        my $sb = stat($file) or croak("Could not stat ($file): $!");
        $atime = $sb->atime;
        $mtime = $sb->mtime;
    } else {
        unless ($self->{_no_create}){
        sysopen my $fh,$file,$SYSOPEN_MODE or croak("Can't create $fil
+e : $!");
        close $fh or croak("Can't close $file : $!");
        $atime = $time;
        $mtime = $time;
        }
    }
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ExtUtils::Command uses:

sub touch {
    my $t    = time;
    expand_wildcards();
    foreach my $file (@ARGV) {
        open(FILE,">>$file") || die "Cannot write $file:$!";
        close(FILE);
        utime($t,$t,$file);
    }
}
[download]

However I can't seem to find what touch() is being used in the case above, but as you can see, the two modules above use a different method to do the work... maybe in that lies the mystery.