People in the past did not consider themselves to have sexual orientations, to be gay or straight or something else. Even someone who was committed to a same-sex romantic relationship wouldn't have, or want, the terminology to describe and identify themselves in those terms. It was... behavior. Passions.
So it's not difficult to see that this lack of labeling and identity would also be a lack of barriers to intimacy and romantic talk without necessitating or implying sexual behavior. If a bro is too proud to sit next to me on a bus bench today because he needs his personal space, perhaps he's afraid of being labeled or branded as something he doesn't like.
I like the fact that the subjects of this article have gone beyond "best friends" terminology and come up with some neat new terms. "Boot-camp besties"! Yeah!