16 million sounds a bit pessimistic to me but maybe they are just trying to be conservative. Or, if the PS5 really releases in late 2019, they are allocating resources to it already. Should be a nice battle between the PS4 and the Switch this year.
They were pessimistic with their forecast last March as well.They increased their forecast by 1M halfway through the FY. By the end of the next FY, the PS4 would have caught up with the Wii.