In the title, the author is seemingly making the claim that all ex-post startup advice is BS. The commenter is debunking that claim by providing sound ex-post advice.
This common-sense interpretation of BS agrees with epistemologists’ definitions of “knowledge”—they invariably define it in such a way that a belief must not only be true, but also true for the right kinds of reasons, to count as knowledge (though there is a lot of disagreement about what those right sorts of reasons are). See for instance the “justified true belief” definition and its critics: https://plato.stanford.edu/entries/knowledge-analysis/
(1) Most startup theory is ex-post, therefore bs.
(2) All ex-post startup theory is bullshit.
Those claims may or may not be true, but there's no contradiction between the two. The title does indeed seem to implicitly claim (2), in the form of the following (implied) syllogism:
Most startup theory is ex-post.
All ex-post startup theory is bullshit.
Therefore, most startup theory is bullshit.
Or, more concisely: most startup theory is ex-post, therefore bs.