Why an array of array preserves my initial array?

Question

So I have this fragment of code:

push @{$savedcallouts[-1]}, {
$funcnm => {
    matches => {%$captures},
    flags => [eval { @flags}]
}};
print Dumper \@{$savedcallouts[-1]};

Which gives the following result:

$VAR1 = [
          [
            {
              'normalexpr' => undef
            },
            {
              'normalexpr' => undef
            },
            {
              'ternaryexpr' => undef
            }
          ]
        ];

But if I remove the square brackets of flags => [eval { @flags}] (i.e. have flags => eval { @flags} - I get this:

$VAR1 = {
          'begin_binary' => {
                              'HASH(0x1038301c0)' => {
                                                       'ternaryexpr' => undef
                                                     },
                              'flags' => {
                                           'normalexpr' => undef
                                         },
                              'matches' => {}
                            }
        };

Any ideas why is this happening and how can I potentially avoid - i.e. have the array as hash field directly without artifacts or being an nested array.