Vault postgres communication

I am reading this blog page PostgreSQL - Database - Secrets Engines | Vault | HashiCorp Developer
At the step 2 Configure Vault with the proper plugin and connection information:

vault write database/config/my-postgresql-database \
    plugin_name="postgresql-database-plugin" \
    allowed_roles="my-role" \
    connection_url="postgresql://{{username}}:{{password}}@localhost:5432/database-name" \
    username="vaultuser" \

In this step does vault tries to connect to the postgres server internally with the given username and password ?