Hi caucatc,
Too much data missing here.
Obviously with lots of fuel on board ZBTJ was filed as ALTN to satisfy legal and company requirements. Were weather conditions at ZBTJ within limits?
Extra fuel on board can be for a number of reasons; tankering (bringing cheaper fuel for the way back or because of fuelling limitations), company requirements, comfort fuel, etc.
Extra fuelling will normally not lead to an overweight situation; if indeed overweight the aircraft would reduce fuel on board through holding or dumping.
Have a chat with the local ops guys at your airfield for more info.
Cheers- Max
