The answer is that you can. He is using anonymous hashes as structs (which is usually the right native Perl data structure to use for that, even though it is not perfect). What strict.pm stops you from doing is making the assumptions that these anonymous things have concrete names in your main namespace - names which you might accidentally use to have one of them override another. (This would be bad.)

my %data;
while (<DATA>) {
   my ($key, $value) = eval $_ or die;
   $data{$key} = $value;
}

print $data{other_key}->[1];    # data

__DATA__
some_key  => { data => 'structure', number => 1 }
other_key => [ qw/ other data structure / ]
third_key => "and a simple third"
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