~Are there private individuals who own and posses such amount of Bitcoin?
Yes, that's for sure.
~Why will one posses such amount as an Individual?
Early adopters and buyers and most likely they've never touched it ever since and have believed or probably have forgotten that they own a lot. Remember that everyone has a timeline when we've bought bitcoin and lucky are those that have bought when it was one, two, three or four digits for its price.
~Are there any consequences to this?
Maybe there is and like how they're going to convert it all at once since policies for huge amount of transactions in exchanges and banks are quite strict.
Another one is the stress, a positive stress on how they're going to spend it.