This is hardly an analog to a black hole. In fact it looks like a well known phenomenon from pipes transmitting sounds (like musical instruments). If you transmit a sound down its length and the end is open, an inverse of the original wave will be transmitted back up the pipe. Similar things happen with an improperly terminated electrical cable.
It's and interesting physics demonstration, but they are extrapolating from a common physical example to try to understand one of the strangest items in the universe.