I hate to say it, but after reading the full story (from which this article is a scanty synopsis), it seems a possible interpretation could be something like the following:
Underage girl meets 18 year old guy. She agrees to go party with him after school. Does so, and does so all night.
Comes home next morning, mother is angry, so she makes an excuse about being "led" to a friend's place and "assaulted" all night.
Her mother then, either because her daughter's acting skills are terrific or because she wants to believe her in order to save her own sense of pride, or even because she understands what I am going to write in the next paragraph, goes and makes the report. If there were another kind of evidence, such as bruises, I did not find it mentioned in the article.
Now, I do not know the truth. I am simply offering a possible interpretation based on what I read. That said, we understand here that despite how conniving and duplicitous the girl could possibly be, a 12 year old is not considered able to consent to sexual activity. Consequently, the young man should not have gotten involved with her no matter how cool she talked and wanted to be, or what she agreed to, promised, or perhaps later lied about. You cannot act upon a child's words in these matters no matter how worldly they may pretend to be. This is why slang terms such as "jail bait" emerged.
Lesson learned for him, I guess, if he can learn. Who knows what punishment he will really get. From what I've seen in the news, it could depend on nothing more than the social standing of the mother vs his family, the personal opinion of the officer, how much money can be paid, or any other reason outside the ethical and healthy basis for consent law. And even were he sent to jail for a time, it doesn't mean he has the capacity to learn. People rationalize anything about their self gratification; adolescent boys even more so.