How does wildcard works?

I have Grafana v.5.2 that uses Elasticsearch 5.5 as datasource. I am trying to use a wildcard search as specified in Lucene documentation. Yet I seem to get strange results.

If you look at this screenshot you’ll see that I am searching for a document wild a field named sender that starts with a substring equal to “AC”, yet none of the returned documents have a sender that starts with “AC”.
Have I missed or misunderstood something?

Shouldn’t it be : (colon) instead of = (equal)?

Sorry, my bad. I had also to remove the “” (quotation mark) in order to get the results. Thanks for help.