It's quite impossible to predict the actual number of people using bobbin because while creating bitcoin wallet and using bitcoin we don't have to provide any person information. Bitcoin account is fully anonymous and we can't count it. Well we could make a smart guess like 2 million or whatever.
Its just an prediction that those number of people would be using bitcoin at a moment and it can be either or higher or lower then 2 million as its impossible to arrive at exact figure of people using it.