This is highly inappropriate. There are proper places for personal and private activities. A girls' bathroom is a public or semi - public space used by multiple people, and engaging in such behavior there is against moral and social norms.
First, they should not encourage or participate in spreading this story. If it is a situation that may be ongoing or a safety issue, they should inform the management or security. They may also need to ensure the privacy and protection of those who may be affected by such a story, and not let it create a negative and judgmental environment.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.
The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.