Earlier quoted context omitted.
Nothing in the OP refers to A/B testing, Usability testing or in fact any kind of testing. At all.
That's irrelevant. There are multiple reasonable possibilities here. Saying "Do X, now get on with coding" as if X is somehow obviously the right answer is a very dangerous attitude. The original article might not have mentioned those kinds of testing explicitly, but still, professionals decide among various choices being considered based on merit, not personal preference.
FWIW I agree with pretty much everything you said in your previous comment (although perhaps not the first sentence).
EDIT: Or perhaps his last sentence irritated you? If he'd omitted "Now, get back to writing code!" would you still feel the same?