Nephi's response is that the words of Isaiah are both literal and figurative. They are literal in that the prophet spoke in a prophetic mode, and is indeed predicting the physical scattering of Israel. While that is easy for the modern world to comprehend, it would have been very difficult for Laman and Lemuel, who had been denying that calamities would occur in Jerusalem. These Isaiah prophecies would appear to bolster Lehi and Nephi's contention that ill would come to Jerusalem, something they had never been able to believe. It is likely in that mode that they ask the question, hoping that the answer would be "spiritual" for that would allow them to continue in their belief that Lehi and Nephi's statements about the destruction of Jerusalem were folly.
The words of Isaiah come home directly to them, however, and Nephi reiterates that this is a literal future event. Nephi does, however, leave open the spiritual interpretation, so that we all might understand that such verses could apply to our own spiritual wanderings and reconciliation.