As he was copying from 𝓞 into 𝓟, Oliver Cowdery accidentally misread nursed as the visually similar nourished. Of course, the semantic possibility of nourished has prevented its discovery as an error, except by reference to the original manuscript.
This passage is an obvious reference to Isaiah’s prophecy just quoted by Nephi:
In addition, just two verses before 1 Nephi 22:8, Nephi refers to this same prophecy, and once more the word used is nursed and not nourished:
Summary: Based on the original manuscript, the verb form nursed should be restored in 1 Nephi 22:8 (“it is likened unto the being nursed by the Gentiles”); the reference here is to the Isaiah quotation in 1 Nephi 21:22–23, which uses the verb nurse, not nourish (“nursing fathers” and “nursing mothers”).