It is tied to the dollar. If 1 bitcoin was not worth a gazillion dollars, no one would be buying or selling it.
The yuan is not tied to the dollar, but can be traded for dollars. Same for Euros, gold, and bricks of heroin.
OK, that last one has to be converted to bitcoin first....
Nothing to do with dollars.
I think you're just using words that you don't really understand. Do you know what a tied currency actually is? They do exist. Do you know what they are?