From what I've seen so far, if I use the OperationResponse.addErrorResult, the process does stop execution, but connector shape is still green, so it's not obvious that an error happened. Usually, if an error happened, the connector shape turns red to indicate so. I also don't see the error in the logs.
I wonder if that is the intended behavior, or if there is something I am missing.
As a workaround, I end the process execution manually by throwing a ConnectorException.