Unfortunately, we do not know the terms of the contract between Hhampuz and BestMixer to arrive at a conclusive determination. I don't believe that Hhampuz should reveal the contract just to satisfy anyone's suspicions. Also, if you look at the last transaction where he paid the signature campaign participants, it lacks a bigger output of ~ .077 BTC that the earlier transactions have. For all we know, the ~.50 BTC covers the pay HHampuz is entitled to under his contract.
Ah yes, Hhampuz was most likely entitled to all of the remaining funds and this is why he took the money and tried to cover his tracks. /s
If you look at all the transactions that he pays participants with, you will see he pays himself out of campaign funds every week this is done either in the same transaction or immediately after the transaction is sent. He was not owed additional money.