Any basis for that assertion?

Not sure whether the Warsaw or Montreal Convention would be applicable here but under either the carrier is responsible for damage resulting from a delay in transportation and there is nothing in either Convention to suggest that "consequential" damages are excluded. It is just the usual question of foreseeability of the damage and whether Royal Brunei took all the (reasonable) necessary steps to avoid the damage.

I would personally try to write a letter to Royal Brunei, explaining that the delay caused the OP to miss the flight he originally booked and ask for reimbursement of the new ticket (s)he had to buy and take it from there.