That's true, this article doesn't cover that at all. But there is growing evidence from other sources that it happened.
That being said, the article gives the time of 10 am as when acts of violence began. If the police did not steer one group to put them into a position to attack the other, then it also did nothing to keep them apart when they had a chance to do so. The accounts given still point to the police doing nothing to keep the groups apart. I accept what is given so far as proof unless authorities can give a better explanation.