Staking more than 1000 coins in one chunk, I don't think so.
It is wasteful to use 1000 coins in only one chunk for staking.
So, if that guy split those coins into 100 chunks for example, he could send some of them out of the wallet without issues.
For coins were immature, he could not send them out of wallet.
I'm not saying they want to stake 1000 coins in 1 chunk I'm saying that's what I think happened. (pretty sure they are trying to setup a masternode and sent 1000 to themselves in 1 chunk)
If you look at the transactions you can see that they had 2 transactions of 0.04998960 which is exactly the reward amount you get from staking. 1000 + 0.04998960 +0.04998960 = 1000.099 as the wallet is set to 2 decimal places by default it will show up as 1000.09, Which is exactly the amount that is Immature and when you have coins that have received a reward for staking but not had the required number of confirmations (102 I believe) they will show up as Immature as soon as 102 has been reached (so on average just under 2 hours) then they will become available again.