Apologies if I’m missing it, but it looks like the claim isn’t specific to men in same-sex marriages.

“Individual gay men earn 10% more than straight men with similar education, experience and job profiles,[2][3] and individual gay men who are married have a significantly higher median income than heterosexual married men.[4]”

I read this as unmarried gay men make 10% more than unmarried straight men, and the number is even higher than 10% for those who are married.