Don't understand if you are being sarcastic. I can say that the giant blobs of XML in our text fields are very annoying. I have to compare them with Kdiff and too many of them don't fit in DBVisualizer's buffer.
I think sarcastic. Psql has great support for json - they were probably taking advantage of it. If you've already got psql set up in your project and have minimal json storage requirements, it can be all you need. You also gain the possibility of retaining some normalization of the data if necessary, which is a lot more complicated if you throw it all in an entirely different database.
Small nit: psql is the command line client bundled with Postgres (PostgreSQL). And yeah, the JSON/JSONB support in Postgres is pretty nifty. Postgres 10 added full text search for JSON/JSONB columns.