as far as I know, users can't withdraw USD (United States Dollar) on Bitfinex, maybe it's USDT but Bitfinex itself believes that 1 USDT will always be worth 1 USD (United States Dollar) 
https://support.bitfinex.com/hc/en-us/articles/213919369-What-are-Tethers-
https://support.bitfinex.com/hc/en-us/articles/213919369-What-are-Tethers-i believe it is because of the old design that they never changed. before Bitfinex started having trouble with their banks last year, they used to have active fiat (USD) markets and small tether on the side. but when the problems began they turned everything into Tether and since they are the creator of Tether too and want to convince the world 1 USDT = 1 USD without implicitly saying it they never changed things in their platform.
I've stopped dealing with bitfinex a long time ago so I didn't know that but it's pretty strange....
If they are showing the price as in USD and actually dealing with USDT, is that even legal?
I'm genuinely amazed by this, they have been operating like this for years and they are still not shut down?
It's clear as day that this is deceiving customers, the same thing that the bshit alliance was doing while misleading customers into buying bshit instead of BTC.