The 1920 LDS edition capitalized the spelling of man, which ends up making the text read as if the people already knew that this individual was the Savior when they first saw him descending from heaven; instead, they thought this man might be an angel until he identified himself as Jesus Christ:
Such capitalization of man has not been introduced elsewhere in the text, as in the following relevant example:
The context is precisely the same as in 3 Nephi 11:8, yet in 1 Nephi 11:7 man has not been capitalized, nor should it be. See under 1 Nephi 1:9 for an example where a twentieth-century LDS edition (in this instance, the 1981) capitalized one because of its eventual reference to deity.
Summary: Restore the lowercase spelling for man in 3 Nephi 11:8 since initially the Nephites did not realize that this individual was Christ.