Hey there. ETF liquidity is largely irrelevant. This is due to the nature of how they're structured.
ETFs use a middle man called an Authorized Participant. When units are needed, the AP will purchase the underlying holdings on the open market, give those holdings to the fund provider, and the fund provider gives the AP units to sell on market.
The reverse is true. When sales are high the AP will go to the fund manager with its ETF units and exchange them for underlying securities, in which it sells on the open market.
This is what keeps ETFs trading near their NAV, and is also why an ETF with 0 daily volume can still be "liquid". Lets take for example a hypothetical S&P 500 ETF that is wildly unpopular for some reason or another. It has 0 traded shares. If someone decided to buy it, the AP would buy the stocks on the S&P 500, go to the fund provider, the fund provider would give them an ETF unit. If you wanted to sell that unit, the process would be as I mentioned above. You still have liquidity, because the underlying stocks are liquid.
Where you get into trouble is when the underlying holdings are NOT liquid. But in the case of ZGQ, this would never be the case.
Hope this makes sense.