I remember hearing from a few years ago, that coinmarketcap had removed some of the chinese (CNY/BTC pairings) exchanges in terms of figuring out how to calculate volume, so recently I had not clicked on the volume link in which it provides more detail regarding how they arrived at volume...

Wow?   I had also not realized how high coinsbank was listed on there (which used to be bitx), and also surprising that localbitcoins is not even listed on there... I suppose no matter what they are attempting to create a somewhat accurate volume indicator, even if they remove some the apparent outliers that would have seemed to have been skewing the numbers.