Why are COLUMN GENERATED ALWAYS AS called "methods" and singled out as a separate field type?
This sounds like you are describing something written. Can you provide a link to where that is?
Is there a common name in the community for the approach in which the data schema is presented as data?
Which community? There are many ways in which a "data schema [can be] presented as data". In PostgreSQL there is only a single source of truth for what the data schema is - the "System Catalogs" [1]. Those tables are made available to the user in the pg_catalog schema.