[ekimekim]

There are two concepts which are being used interchangably here.

The first is JSON as a data encoding, ie. the particular syntax involving braces and quotes and commas and string escapes.

The second is JSON as a data type, ie. a value which may be a string, number, bool, null, array of such values, or map from string to such values. The JSON data type is the set of values which can be represented by the JSON data encoding.

The article describes an optimized storage format for storing values which have the JSON data type. It is not related to JSON the data encoding, except in that it allows input and output using that encoding.

This is the same thing as postgres' JSONB type, which is also an optimized storage format for values of the JSON data type (internally it uses a binary representation).