How did you calculate?
First, this address has 81500 Bitcoins. With the current price of bitcoin, it's 750m dollar.
Second, the address belongs to an exchange. It's clear and there is no doubt.

I believe you are looking at the total received as opposed to the current balance. Over the course of this wallets life 18 billion worth of coins (at todays value) has passed through this address but at this point in time it has around $750 million to its name.

it is not a miracle. if you run a popular services such as an exchange which thousands of people use and deposit their bitcoin with you, you have to store all these bitcoin deposits somewhere safe. and that somewhere safe is a cold stored address like this one here.

And 750m is still a shit ton. And I found out this belongs to a popular gambling website.

You are reading it wrong since if you compute the amount of bitcoins in his address it will not sum up to a billions of dollars. But you are right and you are not dreaming when you saw the 80k plus bitcoins in his wallet address since the blockchain does not lie. You will also be shocked if you will also see a wallet which is a hundred thousand bitcoins on it.

Saints! Where you can earn 81 thousand bitcoins? I don't understand it at all))

It's a gambling website called Carbongaming.ag.. They make bank obviously

It is not from a single person, its probably from a exchange that has huge volume, so this coins belongs to thousand of users not a single one.

Anyway, this is not the richest wallet. Currently this wallet has more than double: https://blockchain.info/address/3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r
The wallet that i mentioned belongs to bitfinex exchange that received more than 1,7million of BTC and has more than 185k BTC now that worth about $1.8 Billion at the moment.

No that is mistake, that adress may have such amount of bitcoin but actually no one has such amount of bitcoin, that belongs to those who use this exchange, is it bitfinex?

This is probably an exchange wallet address,  as an exchange will definitely have alot of traders with so many bitcoins. It simply means, there is no cause for alarm.