The dynamic here is an interesting one. The Lamanites know that they are in the presence of a divine event. It has been preceded by signs that they recognize from their own cultural experience as markers of divinity, the tremblings of the earth. There is also the very obvious danger that they are in as witnessed by the oppressive cloud of darkness. While they do not state that they have fear of the volcano that assuredly produced both the earthquake and the dark cloud, it is quite probable that they also fear the eruption and the potential damage of both the lava and the ash layer. Thus they have a very real concern for their personal welfare.
This concern for personal welfare is not placed in the context of two men who are clearly communing with the divine in the midst of this divine manifestation. The Lamanites do not appear to believe that they may approach Nephi and Lehi directly. Perhaps their shining countenances indicated that they were too close to the divine, and therefore perhaps dangerous by that very proximity to powers that the Lamanites did not well understand. They do need information, however, and so they turn to Aminadab as an interpreter.
This is a new experience for the Lamanites, but they can see that these Nephites have some power that is associated with the divine events. Their logic is that there must be some “Nephite thing” that they could do that might save them from this god-driven fury. It is in this light that they request assistance of Aminadab. Surely he would know the right “Nephite thing” to do so that this crisis might be averted.