Well every user can join the auto exchange feature from the website.
You cann see the auto exchange setting page if you sign in.
As soon as ZEC blocks are found and confirmation is fulfilled, pool send these coins to the highest bid exchange automatically. Pool exchange them to desired coin (what user selected at first), withdraw, and credit to target pool.
So, you mine at ZEC mining pool hub, but you can withdraw them from Bitcoin mining pool hub in BTC.
This was actually intended for auto switching feature, like multipools mining several coins.
Many miners are using this feature for their longer investment.
Many of them mine the most profitable coin like ZEC and get coins into BTC, ETH, or DASH currently.