The price of ETF and the price of underlying are simply correlated as a result of market forces. There's no "tracking" between the two. The only "tracking" happens to the Net Asset Value of the ETF, which the quantitative fund manager must aim to follow the underlying as much as possible. In this case, by holding 100% of asset in Bitcoin in this trust, the NAV tracking can be assumed to be perfect.

The liquidity doesn't matter if the ETF has a fixed pool (with regular creation and redemption). The volume of the ETF can exceed the volumes of all Bitcoin exchanges combined, because the investors are actually trading paper - certificates that represents some units of the trust, which holds Bitcoin.

If creation needs to happen, the investor needs to give the underlying to the trust in exchange for units. In this case, only BTC changes hands.

If redemption needs to happen, the investor will receive the underlying from the trust. In this case, only BTC changes hands.

So, at the trust's side, it's entirely possible to eliminate all fiat transactions after the ETF is issued. All future changes in units will happen with the underlying only, which is Bitcoin. This is similar to and consistent with most of the stock indices ETFs out there in the market.

An analogy: The liquidity of gold ETFs can obviously exceed the liquidity of physical gold. Actually it already does (for retail investors).