I think the same reason as for sweeping #1 - #50: These are bounties - right?
Rico
Amaclin is right. You didn't read (or translate) the question correctly.
The source and the target address in the transaction are the same.
I guess that the reason is to prove they know the private key. I guess that it was found by the large collider thing, since, from what I know, they ask only for a % of the money after "cracking" the private key of a wallet.