I've also not seen that yet on Binance, but it mostly likely will mean this. Maybe its because they havent opened Bitcoin Gold trading until now? Or maybe there are still some fixes to be done to the Bitcoin Gold wallet as it is a new fork.
Not only Binance there are many other exchanges who don't have interest towards the Bitcoin gold. That's why they are adding the pair of Bitcoin gold and Bitcoin in their exchange. I think Bittrex is supporting the pair.
It's a pitty Binance do not make it clear, during the purchasing of Bitcoin Gold, that you will not be able to withdraw it.
Bittrex are currently not trading BTG - they still owe me my forked BTG when I held BTC on the exchange during the fork.