Ujm, halacha is very clear that not returning a goy’s aveidah when failure to do so will result in a chilul Hashem is assur – we must do so to prevent a chilul Hashem. It’s considered a chilul Hashem because it looks like we don’t believe in being honest. We do, just the halacha allows us to keep their aveidos specifically. When a Jewish value is seemingly being violated, even if halachikally it isn’t, it’s a chilul Hashem.
To make a kidush Hashem, it’s allowed to return the aveidah, but it’s not a chiyuv.