“I thought ISIS and the Saudis are at odds.”
Yes and no. ISIS and Sauds are both Sunni Muslim and therefore anti Iran who are Shi’a Muslims, and thus both of their enemies. However, ISIS would like to take over Saudi Arabia that they consider to not be fundamentalist enough and they want to control the holy site of Mecca. So it’s a very mixed bag for Saudi Arabia. I think the Sauds will be secretly relieved if Russia removes the ISIS threat for them without their having to have their fellow Sunni fingerprints on the dirty deed.