No. The norm is follow the gender assumption based on the pseudonym. If the person picked a female name, everyone would happily call the person “she”, as it should be.
However, in an article in which you speculate about the real identity behind a pseudonym, suggesting any possible gender or plurality, you should use /they/, this being the whole point of what your doing.
Can you link a style guide that captures this norm? I usually consider pseudonyms to function like a pointer to the real person when the real person is in scope. If my HN handle was JaneAustism and I was being referenced in a discussion about things pertaining to my meatspace identity and I was a male, I would expect to be described with masculine pronouns. If the discussion was not related to my meatspace identity, I would, in a pseudonymous context, not expect to be referred to as she/her just because my handle contains a female name. My gender is likely irrelevant (or at least unknown) in that context and I would expect they/them.
It’s only inconsistent to you because your understanding of english language usage seems to also be inconsistent (at least with mine, others’ commenting on this thread, and the author’s of the linked article). I find this interesting in the abstract.