The "O" in ORDBMS (Object Relational Database Management System) refers to some object-oriented features in PostgreSQL:
OIDs (mostly deprecated for non-system tables)
User-definable type system including composite types
Context-sensitive operators and functions.
It's up for debate where to draw the line exactly. Here is a recent discussion on the pgsql-advocacy list with more details.
All of this is very different in nature from "ORMs like Hibernate, SQLAlchemy or Doctrine".
An ORM (Object-relational mapping) is trying to translate objects of the respective programming language to relations in a database.