The messages were dropped at the Input because the incoming message had a string where a numeric was expected. A message has to pass through all of Graylog before it is pushed back out to Elasticsearch and potentially get an index error.
Your messages are not making it in to Graylog so you can’t get an index error like the whole “Ignore that” section was talking about.
check out Graylog in a Nutshell to understand message flow a little better.