The OP may have felt slighted, but it was due to envy not math.
The person who won and donated his seal to a friend could just as easily need the seal for himself - and lets face it, he did change his loot preference which I assume meant that he was sacrificing his chance at another drop to get the seal.
The OP voted 'yes' on the loot preference change which modified the odds. (I assume the OP understood this), so where the seal went after it was won, or whether or not the winner actually needed it is completely irrelevant.
In fact, the 'loot preference change' meant that somebody's odds to get another drop may have gone up by the same amount.
As others here have said: If this is a sticking point for you, have the ground rules set up ahead of time and don't change them midstream.
