Not necessarily. Probably 2 of the crewmembers omboard had been on a "short" hop over to New Zealand between the outbound leg and the leg to DXB with a comparably light aircraft.
So, pulling numbers out of a warm spot, if they got a Vr=X for a lightly loaded aircraft for a short leg, then they should have expect to have X+15 for a heavy takeoff. Again, they should have a gut feeling about their results, and if it isn't in the ballpark, they should look at their input and try to figure out where the error lies. Just basic airmanship.