A savings account is generally a no-risk or low-risk investment vehicle. This usually means that you could withdraw the balance on any given day and not suffer a realized loss. Even if you assume that Bitcoin's value will always recover long-term, having short term volatility in the 50% range might mean that the money in a Bitcoin "savings account" will not be available when you actually need it.
I think that's what was meant when calling it digital currency.
But now it's heading down a different path.