The essence of The Boring Company is the same as the business plan behind SpaceX: people assume that an existing industry (tunnel development, rocket launches) is reasonably well run and operating at something of a local optimum. But it turns out that there are order of magnitude (i.e., 10x) improvements available when Musk is able to assemble a sufficiently capable team to focus on it.
I would suggest that tunnelling is a more fertile opportunity, given that there had already been a bunch of rocket startups that had tried and failed over the last couple decades. Tunneling today is insanely expensive. Here's a superb article from Matt Yglesias at Vox on the $2.2 B per km Second Avenue Subway: http://www.vox.com/policy-and-politics/2017/1/1/14112776/new... . Other countries are already achieving costs of $100 M per km or less.
Now, does the car carriage from the video make perfect sense? I'm skeptical. But Musk has never been slavishly faithful to the original conception of his ideas. He gets started and then iterates, and so far the results have been awfully impressive.