Is letting enemy catch up in exp reportable? Isn't it helping enemy team?

Yesterday enemy adc (Sivir) was afk, she came to lane when my Jhin already had lvl5. He decided that he wants to play fair and he let her catch up in exp and gold. Refused to attack her. My support (I don't think they were due) agreed to this. I think it's basically helping enemy team, right? And is should be punishable. I would have no problem with it in normals but in ranked SoloQ?