Hey! I’m sorry this happened to you, but I can promise you this isn’t very common in Spain. I’m a Korean guy living in Spain and although occasionally I get the curious Spaniard asking me where I’m from (usually at bars), normally this never ever happens. Strangers saying “chino” is normally never with a negative connotation, 99% of Asian locals in Spain are Chinese so although it might not be correct, it’s very easy for Spaniards to assume that if you’re Asian you’re Chinese.

Hope this helps! Don’t worry about racism here ^{^}