Prediction: The Boring Company's first tunneling machine will be small-diameter, and each subsequent one will be larger, similar to the scale-up from Falcon 1 to Falcon 9 to Falcon Heavy, simply because that's the right way to do the R&D. But it would be very bad salesmanship to say "the first TBM is really small because that was easier for us", so instead he talks about the benefits of being smaller.