AFAICT the idea originated with Mathematica and Jupyter/IPython was "pretty much like Mathematica".
> And with the release of Mathematica 1.0 in 1988 came another critical element: the invention of Wolfram Notebooks. Notebooks arrived in a form at least superficially very similar to the way they are today (and already in many ways more sophisticated than the imitations that started appearing 25+ years later!): collections of cells arranged into groups, and capable of containing text, executable code, graphics, etc.
That is, consider it as a reference to the specific imitations that started appearing 25+ years later.
I mean, this was obvious to me, but I'm not sure if it's because you're trying to be particularly uncharitable to him for some reason.
While I'm at it: he deserves an uncharitable reading, because he's having a dig at Jupyter (which may be an imitation of Mathematica notebooks) and neglecting to mention any influence of previous work on Mathematica notebooks, such as Knuth's literate programming.