he fluent API is a way to create process definitions using code. This is just what you are doing. What Salaboy says is that this API doesn't cover all the fuctionalitites in bpmn2.
The usual way to work with jBPM5 is to define your processes in .xml files. The syntax of this file is BPMN2. Please take a look at jBPM5 documentation for further details.