Well... I guess most of the times if e.g. a man and a woman are sitting at a restaurant together, people assume that these two are a couple.
Even though these two could actually just be friends or siblings or something.
Like there was a time when I was at a café together with a guy, who I'm in a platonic relationship with. (I wouldn't say that we are friends.)
And I was wondering if we would be mistaken as being a couple.
I remember when I was an early teen and sitting in class, being like "I want a friend."
I think some of my male classmates were like "I can be your friend", and I refused to be friends with them, because I guess I thought boys were only for boyfriend. But well... I didn't feel like they genuinely meant it because most of my male classmates bullied me.
Despite the fact that when I was a child, I used to play with the other children, including boys, in the neighbourhood and we were kinda friends.
And I know that there is the "friends-to-lovers" trope in some medias, where the girl and the boy are good friends and then they become more than friends. And I guess that in some media, a straight girl and a straight boy being just friends and staying just friends must be rare (even though some people probably would be shipping them).
I have heard that for some gay couples, they sometimes get mistaken as being friends or siblings by strangers.