Cluster name in config file not updated (first install)

Hi,
I am running Ubuntu 16.04 LTS.
I have started to install Graylog which need Elasticsearch, following this tutorial (http://docs.graylog.org/en/2.1/pages/installation/os/ubuntu.html).
As it says, in the /etc/elasticsearch/elasticsearch.yml config file, I set "graylog" as for cluster.name.

But when I do curl 'localhost:9200' I get the output

"name" : "Topaz", "cluster_name" : "elasticsearch", ...

The cluster name is not the one I have set up.

Doing systemctl daemon-reload or systemctl enable elasticsearch.service or systemctl start elasticsearch.service does not fix it.

I cannot find any similar problem on internet. I guess the fix is super easy but I can't figure it out.
Thanks in advance