mo2gu started out as a term for a very specific kind of mushrooms, that may have been new to Chinese, but was soon generalized to mean mushroom in general - mushrooms were certainly present in pre-contact environment
Source words
moku [mo:k] 'kind of dried mushroom from Zhangjiakou: kou3mo2); xun4lei4zhiwu „blätterpilzartige“)' Mongolian
