Sql query on elastic 6.8 does not work as expected. Array of nested objects are flattened same as of type object

Question

Thanks for the answer in advance.

I am running a query

SELECT key
FROM records_index
WHERE
  (product_nested_field.code = '1234' and product_nested_field.codeset = 'category1' OR product_nested_field.code = '444' and product_nested_field.codeset = 'category1')
  AND (role_name IN ('user', 'admin'))
GROUP BY records_uuid

In records_index I have record with two products

[
  {codeset: category1, code:444}, 
  {codeset: category2, code:1234}
]

The problem is that query does find a specified record. such behavior is expected for "type": "object" but why I am getting that result for product_nested_field of type nested?

when I translate SQL to JSON I am getting

        {
          "bool": {
            "must": [
              {
                "bool": {
                  "must": [
                    {
                      "nested": {
                        "query": {
                          "term": {
                            "product_nested_field.codeset": {
                              "value": "category1"
                            }
                          }
                        }
                      }
                    }
                  ]
                }
              },
              {
                "bool": {
                  "must": [
                    {
                      "bool": {
                        "should": [
                          {
                            "nested": {
                              "query": {
                                "term": {
                                  "product_nested_field.code": {
                                    "value": "1234"
                                  }
                                }
                              }
                            }
                          },
                          {
                            "nested": {
                              "query": {
                                "term": {
                                  "product_nested_field.code": {
                                    "value": "444"
                                  }
                                }
                              }
                            }
                          }
                        ]
                      }
                    }
                  ]
                }
              }
            ],
            "adjust_pure_negative": true,
            "boost": 1.0
          }
        }

why elastic moves product_nested_field.codeset = 'category1' into separate nested query.