As far as I understand,
AssociationKeyMetadata.getRowKeyColumnNames() contains the name of the columns required to indentify an element in a collection

AssociationKeyMetadata.getColumnNames() contains the columns required to recognize the association

For example, if we have two entity Father (org.hibernate.ogm.backendtck.associations.collection.types.Father) and Child (org.hibernate.ogm.backendtck.associations.collection.types.Child) like the one we are using in the test f for OGM:

AssociationKeyMetadata.getRowKeyColumnNames() contains [Father_id, birthOrder]
AssociationKeyMetadata.getColumnNames() contains only [Father_id]

for bidirectional ManyToMany associations like AccountOwner and BankAccount, the AssociationKeyMetadata.getRowKeyColumnNames() will be the same for both associations:
[owners_id, bankAccounts_id]

AssociationKeyMetadata.getColumnNames() will be [bankAccounts_id] or [owners_id]