I was thinking more in terms of the Wall of Sound as shown in the article. Were they also doing vertical stacks per channel/instrument or were they doing arrays of speakers arranged in a grid per channel/instrument? From what I take it was the later as line arrays weren't a thing at that point, right?
With the Wall of Sound, it worked more-or-less like this:
The bass guitar gets its own pile of speakers. The lead guitar gets its own pile of speakers. The vocals get their own pile of speakers. (And so on, and so forth, until everything on the stage was covered -- maybe with some mixing on a stack to fit something else in, but probably not for things like Jerry's guitar and Phil's bass).
So, yes: There were aspects of the Wall of Sound that absolutely behaved like modern line arrays do (even though "line arrays" as we know and use them today did not begin to gain wide popularity until somewhere around the middle of the 1990s).
There's no magic necessary to implement a line array: It can just be an array of speakers that are arranged in a line.
(Of course, it can also be much, much more complex than that -- but that complexity isn't an inherent part of what a "line array" be. It can involve things like phase-steering and per-element EQ and 3D predictions [and 3D measurements!], but it does not have to be that way in order to be a line array.)
