Do you think the article meant to say it was more likely that the code wasn't inspired by APL?
I do agree that Whitney was inspired to some extent by APL conventions (not exclusively; he was quite a Lisp fan and that's the source of his indentation style when he writes multi-line functions, e.g. in [1]). The original comment was not just a summary of this claim but more like an elaboration, and began with the much stronger statement "The way to understand Arthur Whitney's C code is to first learn APL", which I moderately disagree with.
[0] https://aplwiki.com/wiki/List_of_open-source_array_languages
That's backing for a claim.
Also, I haven't once written APL. I think this might've been borderline trolling, just because of how little investment I have in the topic in reality. Sorry.