Or for some immigrants to change their surnames to blend in with the native peoples. Speaking for myself, when my grandfather immigrated from China to Indonesia, he not only switched his surname from Chen to Tan, but added moar Indonesian-sounding syllables to it. So now we’re disguised as “Sutanto”. Only people who know Chinese would spot the Tan and know we’re Chinese.
(I know, we’re sneaky like that.) Similarly, I have a Chinese-Indo friend whose surname is Halim (added a “Ha” to the original name, which is Lim/Lin).
Sorry for the derail! I don’t think all this is necessary for a side character whose ethnicity is never mentioned, though I maintain it’s always important for the author to have a firm grasp on his characters’s background, even if the reader is never privvy to it.