I think you’re misunderstanding the point the OP is making. Typically, male/female are used when referring to sex, and masculine/feminine and man/woman are used when referring to gender. So this conversation isn’t about gender identity at all, but completely about biological sex.
There are a bunch of factors that go into determining sex. The two main categories are related to the person’s genes (their genotype) and how the person physically presents (phenotype). The biggest genetic marker is whether the person has XX or XY chromosomes (or some other combination). The easiest marker for phenotype is the person’s genitalia, but there are others, such as gonads, gamete production, hormones, etc.
So even just talking about biological sex, a person’s genotype and phenotype might give conflicting determinations of sex. So an “XX male” refers to someone with the genotype of a female, but the phenotype of a male, but says nothing about their gender identity or any surgeries they might’ve undergone.
With that in mind, someone with a PhD in genomics seems to be in the right field to address gene expression and genotypes vs phenotypes. Although you’re right that we shouldn’t rely on authority, but instead on the arguments presented. What we’ve been shown here, though, isn’t a fully fleshed out debate. It’s about 60 words on social media that amounts to “your mental model of sex is wrong; here are cases to rebut it”
Oh, sorry if my response was too basic-level for your experience.
I get what you’re saying about “cis men” being explicitly about gender. I took it as meaning phenotypic males, and that they used “cis men” either for simplicity (perhaps to avoid getting into the details of trans people that they thought was irrelevant to the point they were making) or because they were just imprecise with their language. It’s also possible it was based off of something from earlier in the conversation that we can’t see because it’s just a screenshot.
Anyways, I agree, it was poorly worded, but I think the point they were trying to make was pretty straightforward (unless you insist on interpreting what they said to be something about genes affecting gender expression, then it doesn’t make sense).