The voice recorder actually had the junior copilot strongly and frantically suggesting to the senior pilot that they were flying too low and should climb immediately. The senior pilot curtly overruled him by saying the instruments showed the altitude was fine.
Of course, we will never know what was going on in the junior copilot's mind, but the sequence of events suggests that he had strong reason to feel the altimeter was not functioning correctly and immediate countermeasures were necessary.
Here is that article
Gladwell included a chapter in his book “Outliers” on Korean pilots