moose1am
Everyone in the region has their own little agenda in addition to fighting the more or less universally hated ISIS. In this particular case RuASF was conducting strikes against the anti-Assad and pro Turkey rebels, supported by Turkey with arms and if I remember it right instructors/advisors.
Recently there was a rumour that Turkey deployed ~5k special forces into that (Syrian) area to support rebel operations. At the same time Turkey has very strong anti Kurd interests (because Kurds want an independent state) and were allegedly supporting ISIS financially, view the oil trade.