You could dump the package's symbol table at various places, for example before and after using Class:MethodMaker:

package class;
use Data::Dumper;

BEGIN {
    $Data::Dumper::Sortkeys = 1;
    print 'Before "use Class::MethodMaker": ';
    print Dumper(\%{*class::});
}

use Class::MethodMaker
        get_set      =>  [ qw/ field_1 field_2 field_3 field_4 field_5
+/] ,
        new_with_init =>  'new',
        new_hash_init =>  'hash_init' ;

BEGIN {
    print 'After "use Class::MethodMaker": ';
    print Dumper(\%{*class::});
}

# ...
[download]

The output

Before "use Class::MethodMaker": $VAR1 = {
          'BEGIN' => *class::BEGIN,
          'Dumper' => *class::Dumper
        };
After "use Class::MethodMaker": $VAR1 = {
          'BEGIN' => *class::BEGIN,
          'Dumper' => *class::Dumper,
          'clear_field_1' => *class::clear_field_1,
          'clear_field_2' => *class::clear_field_2,
          'clear_field_3' => *class::clear_field_3,
          'clear_field_4' => *class::clear_field_4,
          'clear_field_5' => *class::clear_field_5,
          'field_1' => *class::field_1,
          'field_1_isset' => *class::field_1_isset,
          'field_1_reset' => *class::field_1_reset,
          'field_2' => *class::field_2,
          'field_2_isset' => *class::field_2_isset,
          'field_2_reset' => *class::field_2_reset,
          'field_3' => *class::field_3,
          'field_3_isset' => *class::field_3_isset,
          'field_3_reset' => *class::field_3_reset,
          'field_4' => *class::field_4,
          'field_4_isset' => *class::field_4_isset,
          'field_4_reset' => *class::field_4_reset,
          'field_5' => *class::field_5,
          'field_5_isset' => *class::field_5_isset,
          'field_5_reset' => *class::field_5_reset,
          'get_field_1' => *class::get_field_1,
          'get_field_2' => *class::get_field_2,
          'get_field_3' => *class::get_field_3,
          'get_field_4' => *class::get_field_4,
          'get_field_5' => *class::get_field_5,
          'hash_init' => *class::hash_init,
          'isa' => *class::isa,
          'new' => *class::new,
          'set_field_1' => *class::set_field_1,
          'set_field_2' => *class::set_field_2,
          'set_field_3' => *class::set_field_3,
          'set_field_4' => *class::set_field_4,
          'set_field_5' => *class::set_field_5
        };
[download]

suggests that the methods are being set up at use time of the module Class::MethodMaker.