As far as I understand, the author argues the typewriters of the era couldn't do that. I have no knowledge about what typewriters existed back then, but any criticism of that claim should also be specific to the time period and not just typewriters in general. (I find it plausible that typewriters in the 60s had the feature you describe, it's just not clear).
For the use of whiteout, for example, the date claim is much more specific in the article.
Having used a typewriter I can confirm what raphlinus wrote above.
Moreover you would not have to use tabs necessarily. A typewriter is an analogue device with a roller on a sled. It's not that there are fixed character cells like in a computer. When you press a button the roller usually moves a fixed distance but you can suppress that and position the roller freely. You also can position your characters freely in the vertical direction by turning the roller with a knob on its side. Basically characters could be placed on the sheet without restrictions. To get an idea what was possible look up Typewriter Art.
For the use of whiteout, for example, the date claim is much more specific in the article.