But it goes beyond just the fact that technology has advanced: Tesla is willing to pursue alternative approaches where others have long stopped (and this is a point the author of this article makes later on). The fact that Tesla doesn't have the conservative culture of other car makers means that they'll make mistakes like this, but also that they'll find new solutions (or recognize existing solutions in similar fields that haven't become industry standard) whereas others would not.
You cannot automate EXISTING car designs much. And Model 3 does make improvements, but in many ways is built similar. It's like trying to automate soldering components by hand. Automation of electronics required a change in the fundamental way electronics were built. Through-hole is hard to automate but relatively easy to build by hand. Surface mount is simple to automate and ultimately better in several ways, but is super annoying to build by hand. Tesla needs to find the surface mount of car manufacturing. And I think they're trying.
Something particularly hard to automate for automobiles is the wire harness. There are many degrees of freedom; it's kind of like tying your shoe: easy for humans, hard for machines. The Model 3 uses less wire than the Model S/X, but only by a factor of 2 or so. Model Y, on the other hand, is supposed to use like an order of magnitude less. This is like optimizing a circuit board for automation by only using a few through-hole components, relying mostly on surface mount.
So Tesla is going to have to continually redesign their vehicles to be more and more amenable to automation. They can't do this as a step function, and Musk has realized that now. (This is another good point the author makes.)