They didn't get a terrian warning because they were landing. Being close to the ground is what they expected. They have both radar & pressure altimeters.
What might have happened is that due to the poor weather they thought they were closer to the airport, or they weren't closely following their glide path, or the aircraft was misconfigured for the RNAV approach. Perhaps a combination of the three.
What might have happened is that due to the poor weather they thought they were closer to the airport, or they weren't closely following their glide path, or the aircraft was misconfigured for the RNAV approach. Perhaps a combination of the three.