Looking at these 2 graphics side by side; if I peg something to the above currency and call it 'stable', I should also be able to peg something to the below currency and call it 'stable', right?
The difference is the time frame: the dollar is quite stable from today to tomorrow, while Bitcoin can easily lose or gain 20%. But I've also seen the dollar (or euro) gain or drop much more than 1% in a day, after some announcement from a central bank.
Now that I think about it, it makes me wonder if Bitcoin is called volatile to distract from the continuous drop in value of fiat money. Fact is: there is no stable currency anymore.