That is not correct, as I said before grep returns a list, and that list is not restricted to be a list of scalars as you are claiming:

update: References are scalars, sorry for the confusion

use strict;
use warnings;
use Data::Dumper;

my @t = (
     [1,2,3],
     0,
     [4,5,6]
    );

my @k = grep { ref $_ eq "ARRAY" } @t;

print Dumper \@k;
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531(255)[1603][/home/pignatelli/tmp]$ perl kkk.pl
$VAR1 = [
          [
            1,
            2,
            3
          ],
          [
            4,
            5,
            6
          ]
        ];
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that list is not restricted to be a list of scalars

Yes it is, as all lists are. You can't have a list of anything but scalars. In your example, grep returned two scalars, both of which are references.