Switching an AC inductive load with a triac largely avoids generating a back emf in the load when it switches off, because a triac will only turn off when the current is near zero. However, a small amount of current (a few mA or tens of mA) will still be passing when the triac turns off, so there sill still be some back emf. Depending on the capacitance of the load, this may be enough to turn the triac on again. That is why a snubber is recommended when switching an inductive load with a triac, unless you have established (e.g. using an oscilloscope) that it is not necessary with a particular load.
Note that the capacitor used in the snubber must have an AC voltage rating sufficient to take the mains voltage. The resistor should also have a sufficient voltage rating, a 1W metal film or wirewound resistor would typically be used.