The correct answer is B. The sentence is using the idiomatic expression: "His mood came out of left field".
An "idiom" is a group of words which, if used in a different context, considering the individual definition of each an every word included in such idiomatic expression, would have another connotation; but once it is considered a local idiom, it shall be understood with its particular meaning.
In this case the idiom: "His mood came out of left field" means that "his anger was completely unexpected or strange."
