신 means God in the Korean dictionary.
I double checked on naver translate and it also means "sour". There are lots of words that have two meanings, just like in English! I think 99.9% of the time you can figure out which meaning is being used with context.
In this case, it's the adjective form of 시다 "to be sour": 시 + ㄴ/은 = 신. Homonyms, brought to you by natural language evolution. :D