If some transmen are attracted to other men they are, by definition, gay. Thus, not all gay men are cisgender. Seems pretty straightforward to me, which is why I acknowledged the existence of gay transmen but didn't make them the focus of my analysis. The sky is self-evidently blue. It doesn't require analysis.

Part of the problem here is the squidgy meaning of terms like "gay," "homosexual," and "transgender." There aren't consistent, consensus agreements on what these terms mean, especially their relationship to concepts like "sex" or "gender."

Example: if your definition of "transgender" encompasses all gender variant or gender non-conforming people, than all gay men are transgender, since the very act of desiring other men is considered gender non-conforming (in societies where sexual desire/behavior is part of gender role expectations). BTW prominent trans-studies scholar Susan Stryker offers this as one acceptable definition of "transgender."

But if you define "transgender" as only those whose gender identity differs from the gender they were labelled at birth, then hardly any gay men—only the transgender ones—are transgender. This also employs one definition of "transgender" offered by Stryker.

This issue is why I went to pains to define the term "cisgender" as I would be using it to answer the question, "Are gay men cisgender?" (Answer: No, they're not.)