There is a big difference between just buying a business class SYD-BNE vs buying a HNL-SYD-BNE ticket

The HNL_BNE fare is not a HNL-SYD fare plus a SYD-BNE fare .

If purchasing just SYD-BNE then indeed there would be a difference in fare

In Feb
BNE-HNL business class r/t is $4000 plus taxes and charges
SYD-HNL business class r/t is $4000 plus taxes and charges

The BNE-SYD-BNE sectors are costing nothing on top on the SYD-HNL-SYD

If the person had purchased separate tickets at $4000 SYD-HNL-SYD plus $1304 for BNE-SYD-BNE, then would definitely be entitled to a reimbursement

Whether the BNE-SYD-BNE is flown in economy or business, there is no difference in price for BNE-HNL r/t