"Gay males who do not identify or express as such" are not actually gay – they're considered "men who sleep with men" or homosexuals. Gay is a chosen identity that piggybacks on msm behaviors, so the idea that the study didn't control for the fact that they're just looking at men who are out seems completely beside the point as it's literally about gay men. (You can be gay and in the closet but not all men who sleep with men identify as gay.)

It's sorta like a study saying "married women get pregnant more often" and then balking that the study didn't control for the fact that women who get married have a second caregiver for a child. Like, yeah, that's the whole point.