I was always under the impression that particular imperial officer was a guy who followed all orders given to him as literally as possible. Afraid to piss off Vader, who is known to kill imperial officers, he was following an order along the lines of "Tractor beam in anyone who tries to escape in a pod." There weren't any life signs, so he didn't bring it in.
There's also a possibility that lots of escape pods were launched as an Imperial does say, "There goes another one!" They might have limited tractor beams so they need to make sure they only lock on to ones with life signs. That might even be a standard operation - fire all the escape pods to create a bunch of clutter so some make it through.
That being said, there is a later line where an officer tells Vader that an escape pod was jettisoned; he seemed to be implying that only one was fired which contradicts the earlier, "There goes another one." Hard to say really.
