It is no surprise to me that using field keys instead of field names reduces queries. If a query needs to be done to get a field and the field name is used ACF must first to a query to get the field key reference as well, 2 queries for each field.
If you must get field values before WP caches the meta values for a post then calling get_post_meta($post_id) will cause WP to cache all meta values for a post and reduce queries because ACF will not cause a query for each field.
