Let’s start with a passage from the essay where Marc is 100% objectively wrong, as a matter of pure logic.
  [...]
  If you argue that AI won’t kill humanity, while simultaneously arguing that “AI will kill humanity” is a category error, your logic is mistaken. Period. End of story.

This isn't the airtight argument the author thinks it is.

It is logically consistent to dismiss an "AI doomer" claim by positing it's based on a category error. That doesn't mean you argue for the exact logical negation of the claims, so you don't automatically grant that it wasn't a category error to begin with.

  Here are examples of what actual category errors look like:
  - “The number two is blue.”

There is a broader, and arguably more common, definition for "category mistake". A statement can be a "category mistake" or not depending on the context. Quoting from <https://plato.stanford.edu/entries/category-mistakes/>:

  For example, an utterance of ‘That is green’ seems infelicitous in a context where the demonstrative refers (or appears to refer) to the number two, but entirely innocuous in a context in which it refers to a pen.

  He spends much time labeling and psychoanalyzing the people who disagree with him

  [...]

  But in the last few years, as his firm a16z took in $7.6B of capital to make a disastrous bet on “Web3”, while charging LPs an estimated $1B in management fees for the privilege, he’s been putting out a stream of disingenuous and logically-invalid arguments.

  For those who didn’t follow Marc’s Web3 debacle, I’ve kept the receipts:

Criticizing pmarca for not engaging with the core of the argument, while simultaneously bringing up "receipts" for unrelated criticisms is odd. This behavior is more consistent with someone who has an axe to grind than with someone who is offended by 'poor “sportsmanship”' in discourse.