I lived in Central America for 4 years, about 3 of which I was an ESL teacher. There are a LOT of Korean textile factories there because of cheaper labor and weaker/unenforced labor laws. But they don't like handing over an ounce of management to locals, so they bring Koreans there to fill in supervisor and manager positions. In turn, their relatives would take advantage of having someone trusted in country closer to the USA, and send their teenagers over to take English classes. So at least 95% of my students were Korean (either working there, kids of workers, or relatives kids sent to study).
I'm grew up in the country side to begin with, and it's just a common habit to nod your head as a greeting or to say thanks. So it wasn't hard to slip me into the habit of a very slight bow as a greeting or gesture of appreciation, as it was only a little more movement than the gesture I grew up with.
However, when I moved back to the USA, I didn't move back to the country side. I live in a suburb between 3 smallish cities. People here give me odd looks when I do that, but even when I only do the head nod. At least older people nod back, or interpret the slight bow as a nod and do the same XD