This is very much true. Since, bitcoins is so much volatile, it is not practical for small transactions.
There is volatility even in American dollar but has been used as an international currency throughout the world for decades. What I want to say is that even with volatility in the price, Bitcoin can be used as a currency and why should one care if it is generally accepted for instant transaction. Tesla is very optimistic about the future of Bitcoin and looks forward to accept the technology for payments.