so how dao work why etheruem is dumped if only dao is hacked?
Because you can split DAO tokens and get your ETH back. So the hacker figured out an exploit that allowed him to gain access to the splitting process to withdraw everyones ETH from the DAO. Obviously this wouldn't be good if he manages to sell them.
according to this it says split on a split on a split on a split he practically just claimed his eth at the maximum amount of eth available for dao if I am right!
An attack has been found and exploited in the DAO, and the attacker is currently in the process of draining the ether contained in the DAO into a child DAO. The attack is a recursive calling vulnerability, where an attacker called the “split” function, and then calls the split function recursively inside of the split, thereby collecting ether many times over in a single transaction