My guess is that they only update that volume number every so often, maybe every 24 hours or so. It would be crazy for the website to update it live. It could just as easily be people placing orders and then quickly deciding they don't want to sell, and then cancelling their orders. From my observations, sometimes it takes a while for the price of some coins to update as well.
I've been doing a lot of research.
I'm sure there was a delay.
thanks for your answer.