Maybe the fuel gauge is faulty. That is really messed up.I guess they thought they can carry kibuyus so when plane stall mid-air they can rush to nearest fueling station and be back soon...to continue with journey.
May be there is a scam involving ground staff. The fuel is pre determined and billed. The KQ staff would have known what is required and ordered the same. There was once such case involving UN planes where they would fill less than they declared and then bill for more. It worked well until the regular pilots went away on emergency replaced by others who not only found the game but reviewed the computer logs versus the bills and boom!
There used to be cases of ground staff under filling the tanks because of discrepancies between Metric and other systems. It caused some disasters. I heard it was changed and made foolproof, leaving deliberate falsification. Anything is possible in India