I'm sure that's are fake payments. They make transfers to their own addresses, then mix them and send them one more time. They just loop it and give it as a payout. Try to track them, and you will see that they are going to nowhere!
Check just few posts from this thread and you will have answer if they are ligit.
Other site actually do that and i will not be surpised if bitminer will fake theirs stats to. We should be aware for that one since surely that payouts are just displayed by them so that they can lure people and scammed them when he right time for them comes so its very better if we just not stick to them since we cannot surely earn some money for that kind of scheme.