I think his hostility comes from the fact that if you google just "postgresql json" the second hit is the official documentation that goes over jsonb right in the second paragraph.

http://www.postgresql.org/docs/9.4/static/datatype-json.html

You can also see that the very first link outside of the official documentation:

https://www.compose.io/articles/is-postgresql-your-next-json...

Explains the benefits of jsonb and how to use indexes.

If you're going to include a database, at the very least do 20 minutes of research on it. If that can't be given, then just don't include something.

That's like saying "I've just installed MongoDB and read the intro documentation page, I'm now going to benchmark it against a MySQL cluster, which I have years of experience with, and that I helped develop." (E.g.: they developed ArangoDB, so they should be experts in at least that, right?)