Bitcoin is still a decentralized virtual currency and as such can not be classified as a stable coin.
Bitcoin's price can still be influnced by market speculation forces ...so it's not a stable coin .
For me,the first and foremost reason that makes a bitcoin not to be stable is its own volatility.It will experience a lot of fluctuations from time to time so it will never make a coin to be stable.But if bitcoin will be legalized by the government soon,i think this time bitcoin will become a stable one.