I wouldn’t say that the roommate necessarily identifies as male. They say “you don’t really need to be a male” when talking about their male marked ID. They purposefully leave the situation ambiguous, likely to minimize the friction of needing to stay in the “male” dorm. They needed to dorm somewhere, and likely couldn’t stay in the female dorm as someone who was AMAB, so they chose to room with a childhood friend and act coy when pressed about their gender.

There’s also the fact that the author is almost certainly trans herself. She doesn’t advertise her gender on most socials, only having it listed on Pixiv, but a brief look at the past profile pics for her Facebook group paints a timeline. She’s posted a number of gender related comics, including a very dark one about Onimai that I don’t have on my phone right now.

My suspicion is that this comic reflects the cultural context that she currently exists in. Keeping her identity on the downlow allows her femcel shitpost comics like Brainrot GF to reach a wider audience, many of whom still refer to queer characters with slurs. Senukin needs the money and doesn’t need the controversy, so she does exactly what this character does.