Note the italicized phrase. Nephi’s is altering the context of “dust” to be the grave, rather than just humiliation. Perhaps the very reason that Nephi has broken with his apparent exegetical tradition of citing massive context if that he understands that he is altering the context for these verses. Nephi is not citing Isaiah as much as referencing Isaiah. In verse 15 the phrase “brought down low in the dust, even that they are not” references the end of his people. Right after the connection between dust and the end of his people, Nephi mentions the records.
At the beginning of verse 16, Nephi is not citing Isaiah, but rather linking Isaiah’s words into his own prophecy, much as a jazz musician might “quote” a familiar tune as part of his improvisation. The critical phrase is “For those who shall be destroyed.” Nephi absolutely ties the reference to Isaiah with those who “shall be destroyed” which references the destruction of his people. This alteration of the text from Isaiah is not intended to “restore” or “retranslate” Isaiah, but rather to recontextualize Isaiah’s words into a new meaning that fits Nephi’s personal vision of the future.