For his book, Silver interviewed Murray Campbell, one of the three IBM computer scientists who designed Deep Blue, and Murray told him that the machine was unable to select a move and simply picked one at random.

That sounds like two evaluations were equal which led Deep Blue to select one at random (humans often do the same thing). Not sure how this counts as a bug... 

In fact soon after the game people showed that Crafty with modest computing power (at the time) was giving that same move in a very short time. Kasparov picked the wrong move to signify either intervening by humans on IBM's part or a great advancement by computers.