I Google Malaysian 777 type and get 200 ER.
All the references I've seen say it was a 777-200ER. (ER = Extended Range.)
Maximum range 8892 statute miles with a full fuel load.
Supposedly, it was fueled only for its scheduled flight to Beijing (2693 miles).
However, it may have departed KUL with extra fuel, either because Captain Z arranged it somehow, or because Malaysian Airlines doesn't like Beijing's fuel price and sought to minimize the tab for the return trip.