Although some ethnic distinctions existed during this period—such as the difference between light-skinned northern Europeans and sub-Saharan blacks—modern categories of race didn’t yet exist. There was simply no conceptual framework in place to ask the question, “Aren’t you Caucasian?”

This sounds a little silly to me. From the way European and Arab chroniclers describe the Mongols and their appearance, it seems that people back then had a more than robust enough system of racial categorization to separately classify East Asians. More likely Taiwan was simply such a remote, alien place to Europeans that almost none of them had sufficient first- or second-hand knowledge to call Psalmanazar's bluff.

In fact, I suspect that the quoted sentence expresses the author's primary motive for even writing this piece in the first place; namely, to argue - contrary to the entire field of population genetics - that categories like "white" and "Asian" are wholly arbitrary social constructs and that races (or at least white people) don't really exist.