That's a cute writeup, but the author overlooked some important bits of history.
For example, the original use of APL (before it was called APL and before anyone had implemented it as a programming language -- the reason Iverson joined IBM) was to specify the IBM 370 machine architecture.
In other words, it was being used to document how the CPU worked. And it was impressively successful there, distilling a large body of documentation into 2 pages.
This reduction in cognitive load, describing machine structure, is what made it popular back then. And this is what motivated the effort to implement it as a programming language.
(Also, if I understand correctly, there's also a relatively short and direct step from APL to the initial implementation of SQL.)