Yes, it is based solely on real accounts' data. I'm not sure I understand the first part of your question - the data is collected from verified accounts only, and since not all accounts are verified, this doesn't take into account 100% of the accounts connected to Myfxbook. As to Myfxbook, there are both demo and real account types connected, so obviously we don't see a point in basing the data on demo accounts also.
The demo figure is just for informational purposes - since many users are confused by this figure, we've decided to remove it for now.
And as to the last question - currently it's not possible to obtain historical data, but it will added in the future.