Yeah, I'm not entirely sure how they managed to get on BitcoinAverage. As far as I know, they don't have an API that exposes trade-volume. And they're not an actual exchange either, they primarily just follow Bitstamp prices with some of their profit margin added on top.
They have their own
exchange which is about to go live as soon as they get permission from the Dutch Central Bank, which should be somewhere in February. In the meantime they are running with a closed group of traders, which is allowed.
Their own site is reporting a 4
BTC 30d volume (not so strange since they're in a very limited closed beta), quite a bit less than the 200+
BTC reported by BitcoinAverage. Perhaps that BitcoinAverage is actually counting the volume of their regular operation, which works similar to CoinBase (but better) and buys and sells directly rather than facilitating trades between users like a regular exchange.