More to the point, why "assume" one way or the other - why not just ask, if in doubt? But of course that would be a question for them doing it, not you:-).

It might very well be the case that you are literally the first Asian-looking person that they have ever met, who speaks English natively. So merely by being present, you are helping break down cultural barriers and helping them realize that the world is larger than they had assumed:-).

Media, by increasing Asian representation, has also helped broaden people's experiences beyond what they see in their small hometowns. So if you had these experiences as a child, and at least one or perhaps multiple decades have passed since then, it might be far less common today to do that. Especially for younger people who have watched such media (TV, movies, YouTube, Instagram, Tiktok, etc.), and therefore realize that people can come from more diverse backgrounds than literally all of the people that they see around their small area - in their churches, grocery stores, and so on.