Csv output plugin prints all fields though it should print fields which are specified in parameter 'fields'

[ankur.aggarwal (Ankur)]

Logstash (5.2.0)
logstash-input-elasticsearch (4.0.0)
logstash-output-csv (3.0.2)

logstash-input-elasticsearch is used to take data from a particular index and query results 10+ fields. Below output should print only 1 field as given but it prints all fields to the file

output {
csv {
fields => [ "fieldname" ]
csv_options => {"col_sep" => "," "row_sep" => "\r\n"}
path => "/tmp/csv-export.csv"
}
}