They need attention. That’s why they were carrying on in public, sufficient to be noticed by someone driving a bus at the time.
The bus driver should be praised, he did a good thing. Protect the eyes of the innocent. Last year my wife and I were swinging our grandchild on a swing at a children's playground. Two lesbian women made it a point to sit at a bench fifteen feet away and began lustily making out, fondling each other. I went over, got into their faces and chewed them out. (Not that kind of chewing out!) I yelled in their faces for being perverts and to get their filthy act out of there. They want to display perverted stuff within the view of children, to indoctrinate them.