Our fuel requirements in Australia are found in CAR 234 and CAAP 234-1.
Companies will have their own fuel policy but in general, a charter operator (piston) must carry:
On top of flight and alternate fuel:
Fixed Reserves: 45 min at holding rate (1500ft above aerodrome)
Variable Reserves: 15% of flight and alternate fuel
Holding: as required by wx / traffic etc. conditions.
From your info, I can't only assume that on that flight, the aircraft had to plan for an alternate aerodrome that was 45 min away, where the wx conditions had a TEMPO or 60min holding.