Occam's Razor. It was most likely a lost human from a distant land, speaking another language, traveling in an exotic looking vessel. This is a simpler explanation than invoking extraterrestrial life.
¯\_(ツ)_/¯
That said, I would love if it actually were the case that a mysterious woman from, say, the Dutch East Indies — to make up a random, semi-plausible example — really did wash ashore in a Japanese fishing village. Sounds like a sequel to "The Thousand Autumns of Jacob de Zoet" (awesome book by the way).