Someone who's got 1000 bitcoins we should call a thousandaire?
Lol, Yeah we can call them like that also but look the price worth of 1000 btc in fiat then you would call them like that. I think we can call him Digital billionaire.
perfect answer what you told is correct as this is digital world so they will be called as Digital Billionaire, but only on digital world as the price goes up and down so today they are digital billionaire as per fiat currency calculation what if tommorrow or after halving if the price goes down then according to that day calculation he will be called according to that.
So in this digital world you cannot tell or give them any names , it is just better to call them WHALES , as they are holding 1000 + bitcoins