That's overstating and doesn't make much sense, if you follow a present term with a futuristic one. Bitcoin could be the future of the financial system, but a the moment it is not and the USD is the most relevant currency.
President Nayib Bukele is just looking for popularity with statements like these, trying to keep El Salvador on the news with their Bitcoin investment.
The currencies of some countries still use usd for international transactions. So I agree with your opinion, USD will not be extinct he will always be there. Because usd is the currency used by several countries. Saying Bitcoin money of the future, it's legitimate according to him but other people's opinions are certainly different. For 10 years or 20 years I think it's still very difficult to legalize Bitcoin as a legitimate means of payment. I didn't expect much for it, even legalizing Bitcoin as a commodity alone has delighted me. Maybe USD and bitcoin continue side by side and needing each other that would be very good.