O refers to the OOP object, it's the R that's the (relational) database.

I expect the parent meant to write R instead of O. It is misleading as nobody ever maps relational databases. As the parent points out, usually they reach for tablational databases. This project also supports a key/value database. But it does not even support relational databases.

Further, the project is focused on implementing the active record pattern, so it would be more appropriately called an async active record than an "async ORM".

but active record is just one of patterns that can be used to implement an ORM?

Active record traditionally depends on ORM, but cannot implement it. ORM exists at a lower layer of abstraction.