I agree with the visual theory, it adds to the viewer feeling that 'something is up' that begins when Ken greets Jim at the door with a gun at his face.
I suppose there was the possibility that when Ken told Jim he was going back for his lighter, Jim might have wanted to come along with him rather than wait in the car. If the lighter wouldn't be there, Jim might suspect something. But then in that case, Ken would not have been able to trash the office.