1. it is the number or rows for the post.
2. Internally ACF does use a loop, the number stored is the number of time to execute the loop. Picture something like this:
$repeater_name = 'repeater';
$count = intval(get_post_meta($post_id, $repeater, true);
for ($i=0; $<$count; $i++) {
$sub_field_value = get_post_meta($post_id, $repeater.'_'.$i.'_sub_field_name');
}
Without having a count of rows ACF would have no idea how many rows there are. The number of rows must be stored.
