The article doesn't do a good job of making the distinction, but there's a big difference between an evacuated tube and an excavated tube. In the first case, you lay a tube along the ground and suck all the air out. In the second, you have to dig a tunnel underground.

Also as mentioned by others, Musk is apparently not talking about an evacuated tube, but it looks like ET3 is. (Unless the quote from Musk was actually that it's not a tunnel, in which case maybe he was making the same distinction.)