Food is really important in Brunei culture, and it is rude to reject food if it is offered to you. My UBD colleague, Malai Ayla Surya Malai Hj Abdullah, tells me that there is a common saying in Malay, "Jangan tolak rezeki", which might be translated as 'Don't reject good fortune'. In other words, if you are offered something such as food, it could bring bad luck on you if you do not eat it.
She also tells a folk tale about a grain of rice and a mountain of gold. One day, when a fisherman finished his lunch, there was one uneaten grain of rice which he tossed into the river. Feeling dejected, this grain of rice started weeping. Then, as it was floating along in the water, it met a mountain of gold which asked it, "Why are you crying?" When the grain of rice explained that a Bruneian person had declined to eat it and had thrown it away, the mountain of gold said, "I was just going to Brunei. But now I won't, as the people there may not value me. I'd better go somewhere else instead." And this story illustrates why you should never spurn good fortune that comes your way, including food.