Well, without having read it in detail, it could be the unique way it portrays relationships. The title itself 'ek bar kaho tum meri ho' gives an impression of longing and a deep emotional connection, which might be explored in a special way in the novel.
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.