Hey,
Netx time, can you open a new thread for those questions, please. Reviving threads that are almost 1.5 years old might become off-topic really quick.
What Martijn did here, was just checking out the JSON format of the search response and walking through it by using a dot as a field separator.
The syntax above is mustache, which is documented in Elasticsearch core in search templates. You might also want to check out the official mustache docs.
If you have more concrete questions, feel free to ask!
--Alex