someone是單數這沒問題,但妳不能說someone就是男的,因為也可能是女的。標準的指代應當是 he or she,而不是單獨he。 但現代英語裏,可以用they指代he or she,所以這裏they不能算錯,實際上這裏用they比用he更符合現代英語用法。
劍橋詞典裏就收錄了they的壹條註釋:
used to avoid saying "he or she":
"There's someone on the phone for you." "What do they want?"