That's freekin awesome, always nice to see retro electronics still in use. That's by far the oldest piece of gear I've ever seen still working.
He did mention it's analog. Since Its a digital circuit going into it, and since it's just 1's and 0's going out of it. Couldn't they have just used a tube to switch between two circuits. One producing a high and one low. and have an RJ-11 jack on the back.