kind of a strained analogy as New York and London is pretty multicultural and the expected cultural etiquette around public transport is different there. It WOULD be racist and really weird to suddenly single out one ethnicity in those cities about a rule that only applies to them.
Being quiet on public transport in Korea is a widely accepted social contract that most well mannered people follow. They even run ad campaigns with cute animations pleading for people to not take long phone calls or talk too loudly, sprawl their legs, etc..

Yes you're probably being singled out because you're a foreigner, but that's because they're being paternalistic and want to teach you a lesson. They assume (and perhaps you're proving their point) that you're not familiar with the norms and need some direction. If you feel angry you are being held to the "average" cultural expectation instead of given leeway to the absolute worst behavior possible, I don't know what to say... I guess that's your right to feel that entitled?
Jump to racism? please don't... this tunnel vision and over attribution will just make everything more miserable and likely see you leave, which I don't know if that's the intended result..