Brian asked Rick to do a job for him. Once Rick had already quoted and began work on said job, Brian then asked Rick to do something else, a separate job (job 2). Rick quoted separately for job 2 and said he would start it when job 1 was finished.
Job 1 has now been finished and Rick has invoiced Brian for it stating that he'll then begin on job 2 shortly.
Brian has said he will not pay for job 1 until job 2 has been completed.
Rick wants paying for job 1 first as this was a completely separate quote and job and had already begun when Brian asked for job 2.
Who is unreasonable?