Because he heard through the phone, other than the sound of her cooking, there was also an undercurrent of other sound.
The sound was soft and weak. Even he, with exceptional hearing, could barely pick it up, much less a normal person. The sound was out of place. It was something he had not heard around his bungalow for the two years he had stayed there.
The noise on Song Qingchun's end was rather loud because she was in the kitchen. On his end, the staff were working overtime. The sound of printers, people on the phone, secretaries chatting in the break room, the honking of cars outside… they all conspired to muddle his hearing, making it hard for him to discern the source of the incongruent sound from Song Qingchun's end.