during the edo period japan had something like a 3rd gender called washaku which r basically little boys with weird haircut (or in japan eyes sexy haircut)
however, in order 4 a boy 2 grow up into an adult they had 2 have sex (be bottom) with an adult man coz tradition states dat only an adult man can teach a boy how 2 grow up & become a real man xD & usually the peeps who fucks the little boy r generally samurai
i think dis is also where they get the idea dat samurai likes 2 fuck little boys coz of dis tradition
idk what they are stating exactly but they might mean that man x man relationship might have been a norm in some time in Japanese history.
You should check out life of wakashu by Linfamy on youtube. It tells about how in that time boys (who are considered not graduated to adults) are lusted by older men. I'm not sure but Nobunaga and Ranmaru might had a similar relationship.
Ok i did some history researching and MC which is reincarnated as Ranmaru Mori is rumored to have sexual relationship with Nobunaga
He is known to be loyal af and has feminine features so i guess that's where they got the idea
I didn't dig that deep about them so I'm not really sure