I think he's referring to the open orders and/or trades in the statistics section.
I've looked into this briefly and I would assume the data is limited to trades passed through their system to the interbank market. Since they're one of the biggest brokers around their dataset is probably pretty valid and could be representative of the market as a whole, particularly for the more liquid pairs (EURUSD, USDJPY).
Why EURGBP is on instead of GBPUSD baffles me somewhat though?
As for me I don't use it but did consider it a few months ago during development and backt-testing.