Does the din of meis mitzvah apply to a non-Jew? If not why – if the reason is for kavod habreyos shouldn’t that apply any meis?
A number of authorities write that there is a Torah mitzvah to bury non-Jews, just as Jews — see Chasam Sofer (Orach Chaim, end of 208); Dovev Mesharim (1:58, based on Chavas Ya’ir and Ramban); see also Minchas Chinuch in Kometz Ha-Minchah 537. See also She’elas Yaavatz (1:41) and Radak (Yehoshua 8:28).
However, the Rambam writes (Mitzvah 231) that the mitzvah applies specifically to Jews, and this appears to emerge from the Yerushalmi (Nedarim, beginning of Chap. 7).
Yet, even according to the Rambam there is a rabbinic instruction to bury non-Jewish dead (Melachim 10:12), because of Darchei Shalom (the Rambam cites verses indicating that this implies that Shalom is an inherent virtue, and the idea is not only that we must bury their dead to avoid friction).
According to the opinion that the Torah mitzvah does not apply to non-Jews, the reasoning will be that the idea of burying the dead is part of the framework of loving-kindness, which applies specifically between member of the Jewish People, and is not obligatory concerning others.
The Torah certainly cares about the honor of the dead, as we find in the verse specifying that “the hanged man is the curse of G-d.” This idea finds expression in the negative instruction of “lo talin nivlaso,” which might apply to non-Jews as well as Jews (this is the opinion of the Ramban, Devarim 21:22; Rashi, however, appears to limit the idea to Jews). Yet, the positive mitzvah of burying the dead might still not apply to non-Jews.