This is certainly the case where ETOPS configured FUEL minimums for LOW alert are set and the flight is used on non-ETOPS sector.
Please bear in mind that Boeing refers to Operator (AO) as the Operator defines its own fuel policy based on local national legislation which thus may only require an mount less then the one where the alert is triggered.
The reason for referring to Operator is thus to enable the Operator to advise crew this possibility exists under certain conditions on (part of) its fleet. Boeing is unable to comment on Operator procedures as they are not involved in OMA etc defining such, but only to aircraft manufacturer defined manuals, FCTM, FCOM, etc