They will get around to ISIS (the article says that even now 30% of Russian airstrikes are against ISIS), but their priority is the rebel groups in the West (which are closer to unseating Assad).
The Russians are fighting at the strategic level - to cut off all the rebels (including ISIS) from their Turkish support first. When the supply lines are cut, it will be much less costly to overrun ISIS positions (while they are out of ammo and suffering desertions).
The Russians also know that if they take out ISIS first, the Turks, Saudis and Obama will be back to supporting the other groups to overthrow Assad. So they plan to defeat those forces first, and save ISIS for later.
All of this is an information war. We are actually angry that they are also attacking “our” rebels too. Bear in mind McCains boys are literally Al Qeida. Yes, THAT Al Qeida from 9/11.
The truth is that the Russians are hurting the rebels badly and we and the EU and the Saudis and Gulf states deeply resent it.